ath79: move small-flash Engenius boards to tiny

ath79: move small-flash Engenius boards to tiny

This moves some of the Engenius boards from generic to tiny:

 - EAP350 v1
 - ECB350 v1
 - ENH202 v1

For these, factory.bin builds are already failing on master
branch because of the unique situation for these boards:

 - 8 MB flash
 - an extra "failsafe" image for recovery
 - TFTP does not work (barely possible with 600 MTU)
 - bootloader loads image from a longer flash offset
 - 1 eraseblock each needed for OKLI kernel loader and fake rootfs
 - using mtd-concat to make use of remaining space...

The manual alternative would be removing the failsafe partition.
However this comes with the risk of extremely difficult recovery
if a flash ever fails because TFTP on the bootloader is bugged.
Signed-off-by: Michael Pratt <mcpratt@pm.me>
[improve commit message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>