ANDROID: KVM: arm64: Advertise KVM vendor hypercalls to protected guests

Advertise KVM vendor hypercalls (i.e. those hypercalls residing in the
"vendor specific" service range of the SMCCC specification and identified
with KVM's UID) to protected guests from EL2 so that memory sharing
hypercalls can later be probed and utilised without involving the host.

Signed-off-by: Will Deacon <will@kernel.org>
Bug: 209580772
Change-Id: Ic80c2aaeba236f0cbcc515d5787a1a4ad230d1d6
Signed-off-by: Will Deacon <willdeacon@google.com>