arm-trusted-firmware-sunxi: depend on sunxi target

The arm-trusted-firmware-sunxi package is only used by the Allwinner
A64, so only make it selectable for its subtarget sunxi/cortexa53.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Reviewed-by: Jonas Gorski <jonas.gorski@gmail.com>

package/boot/arm-trusted-firmware-sunxi/Makefile

@@ -28,6 +28,7 @@ define Package/arm-trusted-firmware-sunxi
     SECTION:=boot
     CATEGORY:=Boot Loaders
     TITLE:=ARM Trusted Firmware for Allwinner
+    DEPENDS:=@TARGET_sunxi_cortexa53
 endef
 
 export GCC_HONOUR_COPTS=s