x86/msr: Offer CPUID Faulting to PVH control domains

x86/msr: Offer CPUID Faulting to PVH control domains

The control domain exclusion for CPUID Faulting predates dom0 PVH, but the
reason for the exclusion (to allow the domain builder to see host CPUID
values) isn't applicable.

The domain builder *is* broken in PVH control domains, and restricting the use
of CPUID Faulting doesn't make it any less broken.  Tweak the logic to only
exclude PV control domains.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>