ath79: Move TPLink WPA8630Pv2 to ath79-tiny target

ath79: Move TPLink WPA8630Pv2 to ath79-tiny target

These devices only have 6MiB available for firmware, which is not
enough for recent release images, so move these to the tiny target.

Note for users sysupgrading from the previous ath79-generic snapshot
images:

The tiny target kernel has a 4Kb flash erase block size instead
of the generic target's 64kb. This means the JFFS2 overlay partition
containing settings must be reformatted with the new block size or else
there will be data corruption.

To do this, backup your settings before upgrading, then during the
sysupgrade, de-select "Keep Settings". On the CLI, use "sysupgrade -n".

If you forget to do this and your system becomes unstable after
upgrading, you can do this to format the partition and recover:

* Reboot
* Press RESET when Power LED blinks during boot to enter Failsafe mode
* SSH to 192.168.1.1
* Run "firstboot" and reboot

Signed-off-by: Joe Mullally <jwmullally@gmail.com>
Tested-by: Robert Högberg <robert.hogberg@gmail.com>
(cherry picked from commit 44e1e5d153d00915a7e516c9af3f440cbd84cf78)