arm64: mm: preserve 4k mappings for late mappings

There are several features such as CONFIG_FREE_PAGES_RDONLY
which depend on pages being mapped as 4k.
When we creating late mappings ensure that 4K mappings
aren't replaced with block mappings if CONFIG_FORCE_PAGES
is enabled.

Change-Id: I9f1853c71ba6dec92ede869b90e220d63af6ae3e
Signed-off-by: Liam Mark <lmark@codeaurora.org>