bmips: add support for Arcadyan AR7516

bmips: add support for Arcadyan AR7516

The Arcadyan AR7516, AKA Orange Bright Box or EE Bright Box 1, is a wifi
fast ethernet router, 2.4 GHz single band with two internal antennas. It
comes with a horizontal stand black shiny casing.

Newer Bright Box 1 model stands vertically, and comes with a totally
different board inside, not compatible with this firmware.

Hardware:
 - SoC: Broadcom BCM6328
 - CPU: single core BMIPS4350 V7.5 @ 320Mhz
 - RAM: 64 MB DDR2
 - Flash: 8 MB SPI NOR
 - Ethernet LAN: 4x 100Mbit
 - Wifi 2.4 GHz: Broadcom BCM43227 802.11bgn (onboard)
 - USB: 1x 2.0
 - ADSL: yes, unsupported
 - Buttons: 2x
 - LEDs: 9x, power LED is hardware controlled
 - UART: yes

Installation in two steps, new CFE bootloader and firmware:

Install new CFE:
  1. Power off the router and press the RESET button
  2. Power on the router and wait some seconds
  3. Release the RESET button
  3. Browse to http://192.168.1.1, this web interface will offer both
     firmware (“Software”) upgrade and bootloader upgrade; be sure to
     use the bootloader section of the upload form.
  4. Upload the new CFE (availabe at the wiki page)
  5. Wait about a minute for flashing to finish and reboot into the new bootloader.

Install OpenWrt via new CFE web UI:
  1. After installing the new CFE, visit http://192.168.1.1
  2. Upload the Openwrt cfe firmware
  5. Wait a few minutes for it to finish

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