arm/trusted-firmware-a: update TC0 to 2.5

TC0 has been using an intermediate SHA post-2.4 as it needed some commits
that were only in the integration branch.

We now have 2.5 which includes these commits, so move to that release.

Change-Id: Ic56c3daa9a408e837219c4f81d22081bbcc5c56d
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>