ANDROID: KVM: arm64: s2mpu: Implement host stage2 idmap callbacks

Remove the existing 's2mpu_host_stage2_set_owner' hook implementation
and refactor the code to match the prepare/apply split of the generic
IOMMU callbacks for updating host stage-2 mappings.

Bug: 190463801
Signed-off-by: David Brazdil <dbrazdil@google.com>
Change-Id: If550fe2c41198c320559c8125ec9ecc0479eb249