x86: KVM guest: sign kvmclock as paravirt

Currently, we only set the KVM paravirt signature in case
of CONFIG_KVM_GUEST. However, it is possible to have it turned
off, while CONFIG_KVM_CLOCK is turned on. This is also a paravirt
case, and should be shown accordingly.

Signed-off-by: Glauber Costa <glommer@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>