fix(mpam): renamed ENABLE_MPAM_FOR_LOWER_ELS to ENABLE_FEAT_MPAM

Renaming ENABLE_MPAM_FOR_LOWER_ELS to ENABLE_FEAT_MPAM for uniformity
with other feature enablement build flags

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: Ib5044a480ebd1e31260c3ce6a462ba51cb3ccdba
diff --git a/tf_config/fvp-mpam b/tf_config/fvp-mpam
index 87b7553..0a215c4 100644
--- a/tf_config/fvp-mpam
+++ b/tf_config/fvp-mpam
@@ -1,3 +1,3 @@
 CROSS_COMPILE=aarch64-none-elf-
-ENABLE_MPAM_FOR_LOWER_ELS=1
+ENABLE_FEAT_MPAM=1
 PLAT=fvp