KVM: x86: Introduce helper to check if vector is set in Hyper-V SynIC

As a preparation to making Hyper-V emulation optional, create a dedicated
kvm_hv_synic_has_vector() helper to avoid extra ifdefs in lapic.c.

No functional change intended.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20231205103630.1391318-6-vkuznets@redhat.com


Signed-off-by: Sean Christopherson <seanjc@google.com>