arm64: Allow remapping lowmem as 4K pages

For certain debug features the lowmem needs to be
mapped as pages instead of sections. Add config
option to allow remapping of lowmem as 4K pages

Change-Id: I50179311facd91b97ecde720da38ec7e47512e95
Signed-off-by: Neeti Desai <neetid@codeaurora.org>