KVM: x86: Insert "AMD" in KVM_X86_FEATURE_PSFD

Intel and AMD have separate CPUID bits for each SPEC_CTRL bit. In the
case of every bit other than PFSD, the Intel CPUID bit has no vendor
name qualifier, but the AMD CPUID bit does. For consistency, rename
KVM_X86_FEATURE_PSFD to KVM_X86_FEATURE_AMD_PSFD.

No functional change intended.

Signed-off-by: Jim Mattson <jmattson@google.com>
Cc: Babu Moger <Babu.Moger@amd.com>
Message-Id: <20220830225210.2381310-1-jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>