include: uapi: Fix UUID to FFA tuple conversion helper

FFA needs the UUID to be in two 64 bit words. The first of
those words holds byte swapped and shifted components of the
UUID. This change ensures the byte swapping alway happens.

Bug: 380065728
Change-Id: I060e41bcde6e25d2d03bf59fafdf183e2cbd3db2
Signed-off-by: Jay Monkman <jmonkman@google.com>