arm64: Use FEAT_HAFDBS to track dirty pages when available

Some recent arm64 cores have a facility that allows the page
table walker to track the dirty state of a page. This makes it
really efficient to perform CMOs by VA as we only need to look
at dirty pages.

Signed-off-by: Marc Zyngier <maz@kernel.org>
[ Paul: pick from the Android tree. Rebase to the upstream ]
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Link: https://android.googlesource.com/platform/external/u-boot/+/3c433724e6f830a6b2edd5ec3d4a504794887263