KVM: SVM: Skip OSVW MSR reads if current CPU doesn't support the feature

KVM: SVM: Skip OSVW MSR reads if current CPU doesn't support the feature

Skip the OSVW RDMSRs if the current CPU doesn't enumerate support for the
MSRs.  In practice, checking only the boot CPU's capabilities is
sufficient, as the RDMSRs should fault when unsupported, but there's no
downside to being more precise, and checking only the boot CPU _looks_
wrong given the rather odd semantics of the MSRs.  E.g. if a CPU doesn't
support OVSW, then KVM must assume all errata are present.

Link: https://patch.msgid.link/20251113231420.1695919-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>