KVM: x86: add guest_cpuid_is_intel

This is similar to existing 'guest_cpuid_is_amd_or_hygon'

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210401111928.996871-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>