add SPM_REFSPEC parameter to the tf-ci-gateway job

add SPM_REFSPEC parameter to the tf-ci-gateway job to
allow testing a specific refspec from the Hafnium project.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I3e7f9650dc18033fa75b6f28b3c29d036eec68d1
1 file changed