Add CROSS_COMPILE setting

Change-Id: Id967c0de049f653d34f35047639f9bc0611db0ab
diff --git a/debian/rules b/debian/rules
index 56fa9ad..f1e8ae2 100755
--- a/debian/rules
+++ b/debian/rules
@@ -14,7 +14,7 @@
 	dh_auto_clean
 
 override_dh_auto_build:
-	LDFLAGS= CFLAGS= dh_auto_build -- PLAT=imx8mq bl31
+	LDFLAGS= CFLAGS= dh_auto_build -- CROSS_COMPILE=aarch64-linux-gnu- PLAT=imx8mq bl31
 
 override_dh_auto_install:
 	dh_auto_install