bcm63xx: add support for ADB P.DG A4101N A-000-1A1-AE

bcm63xx: add support for ADB P.DG A4101N A-000-1A1-AE

ADB P.DG A4101N A-000-1A1-AE has a similar PCB as the OpenWrt's ADB P.DG A4001N1
with LEDs connected to different GPIO PINs in active low configuration.

Hardware:
* Board ID: 96328avngv
* SoC: Broadcom BCM6328 (rev b0) @ 320MHz, CPU BMIPS4350
* RAM DDR2: 64 Mbyte - Winbond W9751G6KB-25
* Serial flash: 16 Mbyte - Winbond 25Q128BVFG
* Ethernet: 4x Ethernet 10/100 baseT
* Wifi 2.4GHz: Broadcom Corporation BCM43225 Wireless Network Adapter (rev 23)
* LEDs: 1x Power, 1x DSL, 1x Internet, 4x ETH, 1x USB, 1x WLAN, 1x WPS, 1x TEL
* Buttons: 1x Reset, 1x WPS, 1x unnamed
* UART: 1x TTL 115200n8, VCC RX TX GND, on J502 connector

Installation via CFE:
* Stock CFE has to be overwritten with a generic 6328 one that can upload
  .bin images with no signature check (cfe6328_configured.bin)
* Connect a serial port to the board
* Stop the cfe boot process after power on by pressing enter
* Set static IP 192.168.2.10 and subnet mask 255.255.255.0
* Navigate to http://192.168.2.50/
* Upload the OpenWrt image file

A4101N GPIO LAYOUT:

Power            always on
DSL              GPIO483(03)
Internet         GPIO491(11)
ETH1             GPIO505(25)
ETH2             GPIO506(26)
ETH3             GPIO507(27)
ETH4             GPIO508(28)
USB              GPIO490(10)
WLAN             controlled by BCM43225
WPS              GPIO489(09)
TEL              GPIO511(31)

Key RESET        GPIO503(23)
Key WPS          GPIO504(24)
Key unnamed      GPIO492(12)

Signed-off-by: Daniele Castro <danielecastro@hotmail.it>
[Amend commit description, DTS improvements, refresh patches]
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>