uboot-imx6: define 'BUILD_DEVICES' for Toradex Apalis

Without 'BUILD_DEVICES' defined, the U-Boot related package won't be
automatically selected when building for Toradex Apalis device.

Signed-off-by: Piotr Dymacz <[email protected]>

package/boot/uboot-imx6/Makefile

@@ -24,6 +24,7 @@ define U-Boot/apalis_imx6
   NAME:=Toradex Apalis
   UBOOT_IMAGE:=SPL u-boot.img u-boot-with-spl.imx
   UBOOT_MAKE_FLAGS:=SPL u-boot.img u-boot-with-spl.imx
+  BUILD_DEVICES:=apalis
 endef
 
 define U-Boot/mx6cuboxi