ramips: disable A5-V11 by default

Disable the A5-V11 image by default as the device has
insufficient flash space for release build images.

Ref: https://forum.openwrt.org/t/devices-too-big-to-save-overlay/18161/72
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/ramips/image/rt305x.mk

@@ -69,6 +69,7 @@ define Device/a5-v11
 	$$(sysupgrade_bin) | check-size $$$$(IMAGE_SIZE) | poray-header -B A5-V11 -F 4M
   DEVICE_TITLE := A5-V11
   DEVICE_PACKAGES := kmod-usb-core kmod-usb-ohci kmod-usb2
+  DEFAULT := n
 endef
 TARGET_DEVICES += a5-v11