ANDROID: KVM: arm64: Memory top-up request from pKVM relinquish

With the introduction of block mapping for guest stage-2 pgtable,
unmapping may need memory donations for the case where a page table
needs to be installed in lieu of a block mapping.

Even though it is futile to ask for memory donations in order to give
back a single page, it at least ensures this path can always work. This
will later be the responsibility for ballooning to coalesce relinquish
calls into a range.

Bug: 278749606
Bug: 278011447
Change-Id: I2b3797ab5132370d3836bf423142bbe8bb8e349c
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>