sgi/build-test-acs.sh: enable ACS suite for RD-Fremont platform

Add RD-Fremont to the platforms list that this build can be executed
for.

Signed-off-by: Nuno Lopes <nuno.lopes@arm.com>
Change-Id: Ia4ff013a989b9d4daf2e9fcfd08c6b64c5cb372d