ANDROID: KVM: arm64: Merge vmcr/apr save/restore

Merge the functions to save and restore vmcr and apr. This can in some
cases reduce the number of hypercalls necessary to load/put the vgic
state in nVHE and will also ease its management in protected mode later
on.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Bug: 209580772
Change-Id: Id85f0698a7a346282e55c15993c274828bd5309c
Signed-off-by: Will Deacon <willdeacon@google.com>