bcm53xx: add support for Meraki MR26

bcm53xx: add support for Meraki MR26

Meraki MR26 is an EOL wireless access point featuring a
PoE ethernet port and two dual-band 3x3 MIMO 802.11n
radios and 1x1 dual-band WIFI dedicated to scanning.

Thank you Amir for the unit and PSU.

Hardware info:
SOC   : Broadcom BCM53015A1KFEBG (dual-core Cortex-A9 CPU at 800 MHz)
RAM   : SK hynix Inc. H5TQ1G63EFR, 1 Gbit DDR3 SDRAM = 128 MiB
NAND  : Spansion S34ML01G100TF100, 1 Gbit SLC NAND Flash = 128 MiB
ETH   : 1 GBit Ethernet Port - PoE
WIFI1 : Broadcom BCM43431KMLG, BCM43431 802.11 abgn
WIFI1 : Broadcom BCM43431KMLG, BCM43431 802.11 abgn
WIFI3 : Broadcom BCM43428 abgn (1x1:1 - id: 43428)
BUTTON: one reset button
LEDS  : RGB-LED
MISC  : Atmel AT24C64 8KiB EEPROM (i2c - seems empty)
      : Ti INA219 26V, 12-bit, i2c output current/voltage/power monitor
      : TPS23754, High Power/High Efficiency PoE Interface+DC/DC Controller

SERIAL:
	WARNING: The serial port needs a TTL/RS-232 3V3 level converter!
	The Serial setting is 115200-8-N-1. The board has a populated
	right angle 1x4 0.1" pinheader.
	The pinout is: VCC (next to J3, has little white arrow), RX, TX, GND.

This flashing procedure for the MR26 was tested with firmware:
    "22-143410M-gf25cbf5a-asa".
    U-Boot 2012.10-00063-g83f9fe4 (Jun 04 2014 - 21:22:39)

A guide how to open up the device is available on the wiki:
<https://openwrt.org/toh/meraki/mr26>

Notes:
 - The WIFI do work to a degree. Limited to 802.11bg in the 2.4GHz band.
 - the WIFI macs are made up.

0. Create a separate Ethernet LAN which can't have access to the internet.
   Ideally use 192.168.1.2 for your PC. The new OpenWrt firmware will setup
   the network via DHCP Discovery, so make sure your PC is running
   a DHCP-Server (i.e.: dnsmasq)
   '# dnsmasq -i eth# -F 192.168.1.5,192.168.1.50
   Download the openwrt-meraki-mr26 initramfs file from openwrt.org and
   rename it to something simple like mr26.bin. Then put it into the tftp's
   server directory.

1. Disassemble the MR26 device by removing all screws (4 screws are located
   under the 4 rubber feets!) and prying open the plastic covers without
   breaking the plastic retention clips. Once inside, remove the plastic
   back casing. Be careful, there some "hidden" retention clips on both
   sides of the LAN port, you need a light to see those. Next, you want to
   remove all the screws on the outer metal shielding to get to the PCB.
   It's not necessary to remove the antennas!

2. Connect the serial cable to the serial header and Ethernet patch cable
   to the device.

4. Before connecting the power, get ready flood the serial console program
   with the magic:   xyzzy  . This is necessary in order to get into the
   u-boot prompt. Once Ready: connect power cable.

5. If you don't get the "u-boot>" prompt within the first few seconds,
   you have to disconnect and reconnect the power cable and try again.

6. In the u-boot prompt enter:

   setenv ipaddr 192.168.1.4
   setenv serverip 192.168.1.2
   tftpboot ${meraki_loadaddr} mr26.bin; bootm

   this will boot a in-ram-only OpenWrt image.

7. Once it booted use sysupgrade to permanently install OpenWrt.
   To do this: Download the latest sysupgrade.bin file and move
   it to the device. Then use sysupgrade *sysupgrade.bin to install it.

    WARNING: DO NOT DELETE the "storage" ubi volume!

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>