Boot: Replace flash partitioning terminology

This change replaces the slot 0/1 terminology with
primary/secondary slot and replaces FLASH_AREA_IMAGE_0/1
with FLASH_AREA_IMAGE_PRIMARY/SECONDARY. This naming
convention fits better to platforms with multiple images
and it is also an architecture agnostic alternative.

Change-Id: I5def429a076024831a702700736d9769a0b2301f
Signed-off-by: David Vincze <david.vincze@arm.com>
23 files changed