KVM: arm64: THP support for pKVM guests

When a pKVM stage-2 guest abort happens, if that fault is within the
remits of a transparent huge page at stage-1, that entire page is pinned
and we can map the entire range of that huge page at stage-2. The
hypervisor in return installs a block mapping. This reduces TLB pressure
and the number of faults.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>