arm64: Use level-2 for largest block mappings when FEAT_HAFDBS is present

In order to make invalidation by VA more efficient, set the largest
block mapping to 2MB, mapping it onto level-2. This has no material
impact on u-boot's runtime performance, and allows a huge speedup
when cleaning the cache.

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/+/417a73581a72ff6d6ee4b0938117b8a23e32f7e8