fix(build): convert tabs and ifdef comparisons

Make interprets lines prefixed with the tab characters as recipes
(commands to run in the shell). Convert the use of ifdef as this
incorrectly interprets when a flag is disabled i.e.
`ENABLE_FEAT_MPAM=0`.

Change-Id: I5173d18a20ef0e3ffc32f0ffb1e70dc30aa4c4a9
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
diff --git a/make_helpers/arch_features.mk b/make_helpers/arch_features.mk
index f957f0d..a337e76 100644
--- a/make_helpers/arch_features.mk
+++ b/make_helpers/arch_features.mk
@@ -217,13 +217,13 @@
 # Build option to enable MPAM for lower ELs.
 # Enabling it by default
 ifeq (${ARCH},aarch64)
-	ENABLE_FEAT_MPAM		?=	2
+        ENABLE_FEAT_MPAM		?=	2
 else ifeq (${ARCH},aarch32)
-	ifdef ENABLE_FEAT_MPAM
-		$(error ENABLE_FEAT_MPAM is not supported for AArch32)
-	else
-		ENABLE_FEAT_MPAM	:=	0
-	endif
+        ifneq ($(or $(ENABLE_FEAT_MPAM),0),0)
+                $(error ENABLE_FEAT_MPAM is not supported for AArch32)
+        else
+                ENABLE_FEAT_MPAM	:=	0
+        endif
 endif
 
 # Include nested virtualization control (Armv8.4-NV) registers in cpu context.