Add OP-TEE into UEFI builds

OP-TEE is used by ARM-TF when collaborating with Android, for example.
So we need to re-enable building OP-TEE in UEFI builds.

Change-Id: Ic6d1004b1d4b6e8cf7725c4abc2c554324f92e4a
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>