Handle PERF_CAPABILITIES directly in kvm_get_msr_feature() now that the
supported value is available in kvm_caps.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221006000314.73240-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>