ANDROID: KVM: arm64: Allow userspace to receive SHARE and UNSHARE notifications

Expose MEM_SHARE and MEM_UNSHARE hypercalls to the KVM_CAP_EXIT_HYPERCALL
capability, allowing userspace (i.e. the VMM) to mprotect() its own
mapping of the pages based upon changes to the host permissions.

Signed-off-by: Will Deacon <will@kernel.org>
Bug: 209580772
Change-Id: I95890595f8cc5493a5a67636bd22da3cc90a95fc
Signed-off-by: Will Deacon <willdeacon@google.com>