bmips: add support for Netgear DGND3700 v1, DGND3800B

bmips: add support for Netgear DGND3700 v1, DGND3800B

The Netgear DGND3700 v1 and DGND3800B are the same device but with
different factory firmwares. It's an xDSL wifi router with a slim black
shiny casing and 4 PCB internal antennas connected via UFL to a miniPCI
detachable card.

Hardware:
 - SoC: Broadcom BCM6368
 - CPU: dual core BMIPS4350 V3.1 @400Mhz
 - RAM: 128 MB DDR
 - NOR Flash: 32 MB parallel (CFE and OS)
 - NAND flash: 128 MB (empty)
 - Ethernet LAN: 5x 1Gbit
 - Wifi 2.4 GHz: Broadcom BCM43222 802.11bgn
 - Wifi 5 GHz: Broadcom BCM43222 802.11abgn
 - USB: 2x 2.0
 - Buttons: 3x, 1 reset
 - LEDs: 11x
 - UART: yes

Installation via OEM web UI:
  1. Open the Netgear administration web interface, by default:
        http://192.168.0.1
	user: admin
        password: password
  2. Look for "upgrade firmware" and proceed
  3. Wait some minutes until it finishes

Signed-off-by: Daniel González Cabanelas <dgcbueu@gmail.com>