target-i386: Introduce x86_cpu_compat_disable_kvm_features()

Instead of the feature-specific disable_kvm_pv_eoi() function, create a
more general function that can be used to disable other feature bits in
machine-type compat code.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>