UUID's in the device tree files were stored in little endian. So
to keep all entries in these files RFC 4122 compliant, store them in
big endian then convert it to little endian when they are read so they
can be used in the UUID data structure.

Signed-off-by: Ruari Phipps <ruari.phipps@arm.com>
Change-Id: I5674159b82b245104381df10a4e3291160d9b3b5