ar71xx: add kernel support for the EnGenius ESR900

Signed-off-by: Forest Crossman <cyrozap@gmail.com>
Patchwork: http://patchwork.openwrt.org/patch/5714/
[juhosg:
  - drop nvram.c modifications,
  - create a separate kernel patch,
  - use ath79_setup_qca955x_eth_cfg helper,
  - merge esr900_{010,common}_setup functions,
  - statically init AR8327 pad configurations,
  - use pr_err instead of printk]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41640 3c298f89-4303-0410-b956-a3cf2f4a3e73