arm: Allow remapping lowmem as 4K pages

Lowmem is currently mapped with sections (1MB/2MB) whenever
possible due to TLB performance boosts. Sections cannot easily
be changed at runtime however which makes implementing certain
features annoying. Add an option to map lowmem with 4K patches.
This is intended to be used as a debugging feature and should
NOT be used for performance testing.

Change-Id: I9612a99b8e05a022f5ba7e568f21307cf66b5667
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>