feat(bl_common): import BL_NOBITS_{BASE,END} when defined
feat(bl_common): import BL_NOBITS_{BASE,END} when defined

If SEPARATE_NOBITS_REGION is enabled, the platform may need to map
memory specifically for that region. Import the symbols from the linker
script to allow the platform to do so.

Signed-off-by: Samuel Holland <c16aab9fe3288df0fb8fc1d24990a300b6b8f299@sholland.org>
Change-Id: Iaec4dee94a6735b22f58f7b61f18d53e7bc6ca8d

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware