fix(tftf): add pack_realm to all

This patch add pack_realm to target all, in order to build pack realm
to tftf by default when user make without specifying a target

Signed-off-by: Nabil Kahlouche <nabil.kahlouche@arm.com>
Change-Id: Ide20ed994777000111924ee4239b77123a3eeed5
diff --git a/Makefile b/Makefile
index 4af1b2a..29a92f6 100644
--- a/Makefile
+++ b/Makefile
@@ -556,6 +556,7 @@
 	@echo "  PACK REALM PAYLOAD"
 	$(shell dd if=$(BUILD_PLAT)/realm.bin of=$(BUILD_PLAT)/tftf.bin obs=1 \
 	seek=$(TFTF_MAX_IMAGE_SIZE))
+all : pack_realm
 endif
 
 ifeq (${ARCH}-${PLAT},aarch64-tc0)