arm64: Reduce PT size estimation complexity

count_required_pts()'s complexity is high if mappings are not using the
largest possible block size (due to some other requirement such as tracking
dirty pages, for example).

Let's switch to a method that follows the pattern established with
the add_map() helper, and make it almost instantaneous instead of
taking a large amount of time if 2MB mappings are in use instead of
1GB.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
[ Paul: pick from the Android tree. Fixup Pierre's commit. 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/+/5d756d147e31a1cdaaa261a50e526404ca5968f5
Link: https://android.googlesource.com/platform/external/u-boot/+/6be9330601d81545c7c941e3609f35bf68a09059