ath79: do not build TP-Link tiny images by default

For quite some time, the tiny (4M flash) TP-Link sysupgrade and
factory images cannot be built anymore by the buildbots, just
the initramfs-kernel.bin files are still there.

Disable these images for the buildbots and prevent useless builds.

Note that these devices still build fine with default settings,
even for kernel 5.4.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath79/image/common-tp-link.mk

@@ -48,12 +48,14 @@ define Device/tplink-4m
   $(Device/tplink-nolzma)
   TPLINK_FLASHLAYOUT := 4M
   IMAGE_SIZE := 3904k
+  DEFAULT := n
 endef
 
 define Device/tplink-4mlzma
   $(Device/tplink-v1)
   TPLINK_FLASHLAYOUT := 4Mlzma
   IMAGE_SIZE := 3904k
+  DEFAULT := n
 endef
 
 define Device/tplink-8m

target/linux/ath79/image/tiny-tp-link.mk

@@ -157,6 +157,7 @@ define Device/tplink_tl-wa850re-v2
   TPLINK_HWID := 0x08500002
   DEVICE_PACKAGES := rssileds
   SUPPORTED_DEVICES += tl-wa850re-v2
+  DEFAULT := n
 endef
 TARGET_DEVICES += tplink_tl-wa850re-v2