uboot-envtools: add support for ALFA Network AP121F

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

package/boot/uboot-envtools/files/ar71xx

@@ -17,6 +17,7 @@ a40|\
 a60|\
 alfa-ap120c|\
 all0258n|\
+ap121f|\
 ap90q|\
 arduino-yun|\
 cap324|\