treewide: Disable building 8M RAM devices

Following deprecation notice[1] in 21.02, disable target with 8M of RAM

[1] https://openwrt.org/supported_devices/864_warning

Signed-off-by: Felix Baumann <[email protected]>

target/linux/bcm47xx/image/legacy.mk

@@ -315,6 +315,7 @@ define Device/usrobotics_usr5461
   DEVICE_PACKAGES := kmod-b43 $(USB1_PACKAGES)
   IMAGES := bin
   IMAGE/bin := append-rootfs | trx-with-loader | usrobotics-bin
+  DEFAULT := n
 endef
 TARGET_DEVICES += usrobotics_usr5461