SPM: RESET_TO_BL31 add a third cactus partition

A third cactus sample test partition was added to tf-a-tests.
The test fvp-spm-rst-bl31,fvp-default:fvp-spm.rstbl31 requires
the third partition to be preloaded when invoking the model as
BL1/BL2 do not exist in this test case.

Change-Id: I6bcb5b220718880cba8ec6077dd6b8877df8c22b
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/fvp_utils.sh b/fvp_utils.sh
index 9bb8a34..42434dc 100644
--- a/fvp_utils.sh
+++ b/fvp_utils.sh
@@ -22,6 +22,7 @@
 spmc_manifest_addr="${spmc_addr:-0x0403f000}"
 sp1_addr="${sp1_addr:-0x7000000}"
 sp2_addr="${sp2_addr:-0x7100000}"
+sp3_addr="${sp3_addr:-0x7200000}"
 
 ns_bl1u_addr="${ns_bl1u_addr:-0x0beb8000}"
 fwu_fip_addr="${fwu_fip_addr:-0x08400000}"