Revert "arm64: Use FEAT_HAFDBS to track dirty pages when available"

This reverts commit 6cdf6b7a. This is
part of a series trying to make use of the arm64 hardware features for
tracking dirty pages. Unfortunately this series causes problems for the
AC5/AC5X SoCs. Having exhausted other options the consensus seems to be
reverting this series is the best course of action.

Signed-off-by: Chris Packham <judge.packham@gmail.com>