docs: clarify packing of UUID in ffa manifest

Update the ffa-manifest-bindings to clarify how the
Partition property 'UUID' must be packed.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Change-Id: Ic5ee67c9606dec30ed3a3234a5f40a976ecbb72c
1 file changed