BACKPORT: FROMGIT: arm64: mm: Implement arch_wants_old_prefaulted_pte()

On CPUs with hardware AF/DBM, initialising prefaulted PTEs as 'old'
improves vmscan behaviour and does not appear to introduce any overhead
elsewhere.

Implement arch_wants_old_prefaulted_pte() to return 'true' if we detect
hardware access flag support at runtime. This can be extended in future
based on MIDR matching if necessary.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Change-Id: I0cd9ccf68bdd7b55e69306f0bfb3045c93f539fa
Bug: 171278850
(cherry picked from commit 0388f9c7
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/faultaround

)
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>