ath79: use dynamic partitioning for TP-Link CPE series

ath79: use dynamic partitioning for TP-Link CPE series

CPExxx and WBSxxx boards with AR9344 SOC
use the OKLI lzma kernel loader
with the offset of 3 blocks of length 4k (0x3000)
in order to have a fake "kernel" that cannot grow larger
than how it is defined in the now static OEM partition table.

Before recent changes to the mtdsplit driver,
the uImage parser for OKLI only supported images
that started exactly on an eraseblock boundary.

The mtdsplit parser for uImage now supports identifying images
with any magic number value
and at any offset from the eraseblock boundary
using DTS properties to define those values.

So, it is no longer necessary to use fixed sizes
for kernel and rootfs

Tested-by: Andrew Cameron <apcameron@softhome.net>  [CPE510 v2]
Tested-by: Bernhard Geier <freifunk@geierb.de>      [WBS210 v2]
Tested-by: Petrov <d7c48mWsPKx67w2@gmail.com>       [CPE210 v1]
Signed-off-by: Michael Pratt <mcpratt@pm.me>
(cherry picked from commit 7b9a0c264cb9dc2c5a946a0aa9a290427a5e559c)