This patch adds a platform setup handler that gets called after
the MMU is enabled. Platforms wanting to make use of this handler
should declare 'plat_late_platform_setup' handler in their platform
files, to override the default weakly defined handler.

Change-Id: Ibc97a2e5a24608ddea856d0bd543a9d5876f604c
Signed-off-by: Dilan Lee <dilee@nvidia.com>