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 - Add support for loading a BL3-0 image in BL2. Information about
   memory extents is populated by platform-specific code. Subsequent
   handling of BL3-0 is also platform specific.
   The BL2 main function has been broken down to improve readability.
   The BL3-2 image is now loaded before the BL3-3 image to align with
   the boot flow.

 - Build system: Add support for specifying a BL3-0 image that will be
   included into the FIP image.

 - IO FIP driver: Add support for identifying a BL3-0 image inside a
   FIP image.

 - Update the documentation to reflect the above changes.

Change-Id: I067c184afd52ccaa86569f13664757570c86fc48