KVM: arm64: Reload stage-2 for VMID change on VHE

Naturally, a change to the VMID for an MMU implies a new value for
VTTBR. Reload on VMID change in anticipation of loading stage-2 on
vcpu_load() instead of every guest entry.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231018233212.2888027-4-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>