ANDROID: BACKPORT: mm/vmalloc: Add arch-specific callbacks to track io{remap,unmap} physical pages

Add a pair of hooks (ioremap_phys_range_hook/iounmap_phys_range_hook)
that can be implemented by an architecture. Contrary to the existing
arch_sync_kernel_mappings(), this one tracks things at the physical
address level.

This is specially useful in these virtualised environments where
the guest has to tell the host whether (and how) it intends to use
a MMIO device.

Signed-off-by: Marc Zyngier <maz@kernel.org>
[willdeacon@: Hook ioremap_page_range() in mm/ioremap.c]
Bug: 209580772
Change-Id: I970c2e632cb2b01060d5e66e4194fa9248188f43
Signed-off-by: Will Deacon <willdeacon@google.com>