spapr_pci: Use XICS interrupt allocator and do not cache interrupts in PHB

Currently SPAPR PHB keeps track of all allocated MSI (here and below
MSI stands for both MSI and MSIX) interrupt because
XICS used to be unable to reuse interrupts. This is a problem for
dynamic MSI reconfiguration which happens when guest reloads a driver
or performs PCI hotplug. Another problem is that the existing
implementation can enable MSI on 32 devices maximum
(SPAPR_MSIX_MAX_DEVS=32) and there is no good reason for that.

This makes use of new XICS ability to reuse interrupts.

This reorganizes MSI information storage in sPAPRPHBState. Instead of
static array of 32 descriptors (one per a PCI function), this patch adds
a GHashTable when @config_addr is a key and (first_irq, num) pair is
a value. GHashTable can dynamically grow and shrink so the initial limit
of 32 devices is gone.

This changes migration stream as @msi_table was a static array while new
@msi_devs is a dynamic hash table. This adds temporary array which is
used for migration, it is populated in "spapr_pci"::pre_save() callback
and expanded into the hash table in post_load() callback. Since
the destination side does not know the number of MSI-enabled devices
in advance and cannot pre-allocate the temporary array to receive
migration state, this makes use of new VMSTATE_STRUCT_VARRAY_ALLOC macro
which allocates the array automatically.

This resets the MSI configuration space when interrupts are released by
the ibm,change-msi RTAS call.

This fixed traces to be more informative.

This changes vmstate_spapr_pci_msi name from "...lsi" to "...msi" which
was incorrect by accident. As the internal representation changed,
thus bumps migration version number.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[agraf: drop g_malloc_n usage]
Signed-off-by: Alexander Graf <agraf@suse.de>
