ath79: enable all space on Netgear ar9344-based WNDR routers

ath79: enable all space on Netgear ar9344-based WNDR routers

Netgear WNDR routers (AR9344 models) like WNDR4300 have 128 MiB of flash
memory but only first 32 MiB are used now - both by vendor's firmware and
OpenWrt. This patch concatenates two regions of flash memory: ubi part
of firmware partition and reserved (unused) space beyond 'caldata_backup'
while preserving ART backup. No data is wiped or moved away.
This increases area for OS ubi volumes from 23 to 119 Megabytes.

Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>