[TEMP] don't include RMM as part of FIP binaries

RMM image authentication with TBBR fails. The COT for RMM enabled
platform should be CCA. For now, RMM image is loaded in backdoor using
model script and image autheticaion for RMM image is skipped in TF-A.

Once the RMM image authentication in TF-A will be functional, this patch
can be reverted.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: I503a0588b3d9a6a9198eef5053facae0d488a724