KVM: arm64: Distinct pKVM teardown memcache for stage-2

In order to account for memory dedicated to the stage-2 page-tables, use
a separated memcache when tearing down the VM. Meanwhile rename
reclaim_guest_pages to reflect the fact it only reclaim page-table
pages.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250313114038.1502357-3-vdonnefort@google.com


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>