ANDROID: KVM: arm64: Introduce concept of pKVM moveable regions

The pKVM memory pool is currently sized to allow page-granularity
mapping in the host stage-2 page-table of all the memory as well as up
to 1GiB of MMIO range. Indeed, pKVM currently assumes that MMIO regions
are completely and solely owned by the host for the entire lifetime of
the system. As such, the pages used to map MMIO regions can always be
recycled to allow forward progress if the memory pool ran out of
pages -- pKVM can unmap MMIO ranges at stage-2 without fearing to loose
important information about the state of the underlying page, and those
mappings can always be reconstructed later.

In order to allow transitioning the ownership of non-memory regions,
introduce a concept of pkvm 'moveable' regions, which represents regions
of the physical address space which can be 'moved' from an ownership
perspective. These moveable regions are used to size the hyp memory
pool. In a first step, the list of moveable regions is equal to the
memblock list, but it will be extended in subsequent changes.

No functional changes intended.

Bug: 244543039
Bug: 244373730
Change-Id: I7f451924b1eed9579868e6ff8c7adc7b4a5a0ae1
Signed-off-by: Quentin Perret <qperret@google.com>