sysbus: Set user_creatable=false by default on TYPE_SYS_BUS_DEVICE

commit 33cd52b5d7b9adfd009e95f07e6c64dd88ae2a31 unset
cannot_instantiate_with_device_add_yet in TYPE_SYSBUS, making all
sysbus devices appear on "-device help" and lack the "no-user"
flag in "info qdm".

To fix this, we can set user_creatable=false by default on
TYPE_SYS_BUS_DEVICE, but this requires setting
user_creatable=true explicitly on the sysbus devices that
actually work with -device.

Fortunately today we have just a few has_dynamic_sysbus=1
machines: virt, pc-q35-*, ppce500, and spapr.

virt, ppce500, and spapr have extra checks to ensure just a few
device types can be instantiated:

* virt supports only TYPE_VFIO_CALXEDA_XGMAC, TYPE_VFIO_AMD_XGBE.
* ppce500 supports only TYPE_ETSEC_COMMON.
* spapr supports only TYPE_SPAPR_PCI_HOST_BRIDGE.

This patch sets user_creatable=true explicitly on those 4 device
classes.

Now, the more complex cases:

pc-q35-*: q35 has no sysbus device whitelist yet (which is a
separate bug). We are in the process of fixing it and building a
sysbus whitelist on q35, but in the meantime we can fix the
"-device help" and "info qdm" bugs mentioned above. Also, despite
not being strictly necessary for fixing the q35 bug, reducing the
list of user_creatable=true devices will help us be more
confident when building the q35 whitelist.

xen: We also have a hack at xen_set_dynamic_sysbus(), that sets
has_dynamic_sysbus=true at runtime when using the Xen
accelerator. This hack is only used to allow xen-backend devices
to be dynamically plugged/unplugged.

This means today we can use -device with the following 22 device
types, that are the ones compiled into the qemu-system-x86_64 and
qemu-system-i386 binaries:

* allwinner-ahci
* amd-iommu
* cfi.pflash01
* esp
* fw_cfg_io
* fw_cfg_mem
* generic-sdhci
* hpet
* intel-iommu
* ioapic
* isabus-bridge
* kvmclock
* kvm-ioapic
* kvmvapic
* SUNW,fdtwo
* sysbus-ahci
* sysbus-fdc
* sysbus-ohci
* unimplemented-device
* virtio-mmio
* xen-backend
* xen-sysdev

This patch adds user_creatable=true explicitly to those devices,
temporarily, just to keep 100% compatibility with existing
behavior of q35. Subsequent patches will remove
user_creatable=true from the devices that are really not meant to
user-creatable on any machine, and remove the FIXME comment from
the ones that are really supposed to be user-creatable. This is
being done in separate patches because we still don't have an
obvious list of devices that will be whitelisted by q35, and I
would like to get each device reviewed individually.

Cc: Alexander Graf <agraf@suse.de>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Alistair Francis <alistair.francis@xilinx.com>
Cc: Beniamino Galvani <b.galvani@gmail.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Frank Blaschka <frank.blaschka@de.ibm.com>
Cc: Gabriel L. Somlo <somlo@cmu.edu>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Pierre Morel <pmorel@linux.vnet.ibm.com>
Cc: Prasad J Pandit <pjp@fedoraproject.org>
Cc: qemu-arm@nongnu.org
Cc: qemu-block@nongnu.org
Cc: qemu-ppc@nongnu.org
Cc: Richard Henderson <rth@twiddle.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Shannon Zhao <zhaoshenglong@huawei.com>
Cc: sstabellini@kernel.org
Cc: Thomas Huth <thuth@redhat.com>
Cc: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
Acked-by: John Snow <jsnow@redhat.com>
Acked-by: Juergen Gross <jgross@suse.com>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-3-ehabkost@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[ehabkost: Small changes at sysbus_device_class_init() comments]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
