target-i386: kvm: Enable all supported KVM features for -cpu host

When using -cpu host, we don't need to use the kvm_default_features
variable, as the user is explicitly asking QEMU to enable all feature
supported by the host.

This changes the kvm_cpu_fill_host() code to use GET_SUPPORTED_CPUID to
initialize the kvm_features field, so we get all host KVM features
enabled.

This will also allow us to properly check/enforce KVM features inside
kvm_check_features_against_host() later. For example, we will be able to
make this:

  $ qemu-system-x86_64 -cpu ...,+kvm_pv_eoi,enforce

refuse to start if kvm_pv_eoi is not supported by the host (after we fix
kvm_check_features_against_host() to check KVM flags as well).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
