KVM: x86: Turbo bits in MSR_PLATFORM_INFO

Allow userspace to set turbo bits in MSR_PLATFORM_INFO. Previously, only
the CPUID faulting bit was settable. But now any bit in
MSR_PLATFORM_INFO would be settable. This can be used, for example, to
convey frequency information about the platform on which the guest is
running.

Signed-off-by: Drew Schmitt <dasch@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>