arm64: KVM: Add support for 16-bit VMID

The ARMv8.1 architecture extension allows to choose between 8-bit and
16-bit of VMID, so use this capability for KVM.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
(cherry picked from commit 20475f78)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

Conflicts:
	camptiable with LTS 849e28ef:arm64: KVM: Configure TCR_EL2.PS at runtime
	in arch/arm64/kvm/hyp-init.S