fix(realm): add BP_OPTION to REALM_CFLAGS

Adds missing BP_OPTION to REALM_CFLAGS to
allow build realm payload with BTI/Pauth support.

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: I52bb24ffff9d662fee30706290805c455dc3137a
diff --git a/Makefile b/Makefile
index fa48787..13aeef9 100644
--- a/Makefile
+++ b/Makefile
@@ -255,6 +255,7 @@
 CACTUS_MM_CFLAGS	+= -mbranch-protection=${BP_OPTION}
 CACTUS_CFLAGS		+= -mbranch-protection=${BP_OPTION}
 IVY_CFLAGS		+= -mbranch-protection=${BP_OPTION}
+REALM_CFLAGS		+= -mbranch-protection=${BP_OPTION}
 endif
 
 ifeq ($(SMC_FUZZING), 1)