lantiq: add support for FritzBox 7312

lantiq: add support for FritzBox 7312

The FritzBox 7312 is also known as 1&1 WLAN-MODEM. The device is almost
the same as FB7330, but only one ETH-Port and no USB.

Hardware
SoC: Lantiq Xway ARX188 PSB 50812 EL
RAM: 64MB DDR1 (Zentel A4S12D40FTP-G5)
Ethernet: Atheros 8030
Wireless: Atheros AR9227 b/g/n 2x2
DSL: Lantiq ADSL2+
DECT: Dialog SC14441
Buttons: WiFi, DECT
LEDs: Power/DSL, Fon, DECT, WLAN, Info

LEDs
Power: GPIO#44 (active low)
Internet: GPIO#47 (active low)
DECT: GPIO#38 (active low)
WLAN: GPIO#37 (active low)
Info: GPIO#35 (active low)

The Fon LED is labeled as internet in avm gpl sources.

Buttons
WLAN: GPIO#1 (active low)
DECT: GPIO#2 (active low)

Phy
GPIO#03: 25 MHz
GPIO#34: Reset (active low)
GPIO#39: Int
GPIO#42: MII MDIO
GPIO#43: MII MDC

PCIe
GPIO#21: reset (active low)

Installation:

To install OpenWrt via Eva bootloader, within the first seconds after
power on a ftp connection need to be established to the FRITZ!Box at
192.168.178.1 and the the following ftp commands need to be run:

  ftp> quote USER adam2
  ftp> quote PASS adam2
  ftp> binary
  ftp> debug
  ftp> passive
  ftp> quote MEDIA FLSH
  ftp> put /path/to/openwrt-lantiq-xway-avm_fritz7312-squashfs-sysupgrade.bin mtd1
  ftp> quote REBOOT

Signed-off-by: Johann Neuhauser <johann@it-neuhauser.de>