ANDROID: KVM: arm64: Add MEMINFO and {UN,}SHARE hypercalls for protected guests

Expose the __pkvm_guest_{un,}share_host() functionality to protected
guests in the form of three new hypercalls in the KVM vendor service
range:

  - HYP_MEMINFO: Query the size of the sharing granule (i.e. the stage-2
                 page size)

  - MEM_SHARE: Share a page back with the host, granting RWX permission.

  - MEM_UNSHARE: Remove host access to a page previously shared with
                 MEM_SHARE.

Signed-off-by: Will Deacon <will@kernel.org>
Bug: 209580772
Change-Id: Ie5a1f215058df6738e1d4f357497c82b8617c765
Signed-off-by: Will Deacon <willdeacon@google.com>