acs: build Hafnium for FVP platform

FF-A ACS test suite only requires the Hafnium SPMC binary for FVP.
Omit building the test framework as this is unused in this environment.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: Ie25b27f023a117cc74b6204f1dcef5741ba1051f
diff --git a/acs/builder.sh b/acs/builder.sh
index 716daab..cd8c567 100755
--- a/acs/builder.sh
+++ b/acs/builder.sh
@@ -21,7 +21,7 @@
 
 cd ${WORKSPACE}/hafnium
 echo "Building Hafnium."
-make PROJECT=reference
+make PLATFORM=secure_aem_v8a_fvp_vhe
 
 # Build TF-A
 cd ${WORKSPACE}/trusted-firmware-a