ANDROID: KVM: arm64: Let modules specify arbitrary permissions for host pages

Currently pKVM modules can only restrict the host stage-2 permissions of
some pages with no way of relaxing them later on. Also, modules lack the
ability to unmap pages from the host without mapping them in the
hypervisor as they only have access to the host-to-hyp-donation path.

In order to give modules more flexibility, make the
hyp_protect_host_page() function a lot more generic by allowing it to
relax permissions as well as "map" with !R!W!X.

Bug: 264070847
Change-Id: Id6751fe147ea8b86a416a1c3326a2d75f04b623d
Signed-off-by: Quentin Perret <qperret@google.com>