Replaced PLAT_ARM_FIP_BASE and PLAT_ARM_FIP_MAX_SIZE macro with a
generic name PLAT_ARM_FLASH_IMAGE_BASE and PLAT_ARM_FLASH_IMAGE_MAX_SIZE
so that these macros can be reused in the subsequent GPT based support
changes.

Change-Id: I88fdbd53e1966578af4f1e8e9d5fef42c27b1173
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>