ipq40xx: add support for AVM FRITZ!Repeater 3000

ipq40xx: add support for AVM FRITZ!Repeater 3000

Hardware
--------
CPU:   Qualcomm IPQ4019
RAM:   256M (NANYA NT5CC128M16JR-EK)
FLASH: 128M NAND (Macronix MX30LF1G18AC-XKI)
ETH:   Qualcomm QCA8072
WiFi2: IPQ4019 2T2R 2SS b/g/n
WiFi5: IPQ4019 2T2R 2SS n/ac
WiFi5: QCA9984 4T4R 4SS n/ac
LED:    - Connect green/blue/red
        - Power green
BTN:   WPS/Connect
UART:  115200n8 3.3V
       VCC - RX - TX - GND (Square is VCC)

Installation
------------
1. Grab the uboot for the Device from the 'u-boot-fritz3000'
   subdirectory. Place it in the same directory as the 'eva_ramboot.py'
   script. It is located in the 'scripts/flashing' subdirectory of the
   OpenWRT tree.

2. Assign yourself the IP address 192.168.178.10/24. Connect your
   Computer to one of the boxes LAN ports.

3. Connect Power to the Box. As soon as the LAN port of your computer
   shows link, load the U-Boot to the box using following command.

   > ./eva_ramboot.py --offset 0x85000000 192.168.178.1 uboot-fritz3000.bin

4. The U-Boot will now start. Now assign yourself the IP address
   192.168.1.70/24. Copy the OpenWRT initramfs (!) image to a TFTP
   server root directory and rename it to 'FRITZ3000.bin'.

5. The Box will now boot OpenWRT from RAM. This can take up to two
   minutes.

6. Copy the U-Boot and the OpenWRT sysupgrade (!) image to the Box using
   scp. SSH into the Box and first write the Bootloader to both previous
   kernel partitions.

   > mtd write /path/to/uboot-fritz3000.bin uboot0
   > mtd write /path/to/uboot-fritz3000.bin uboot1

7. Remove the AVM filesystem partitions to make room for our kernel +
   rootfs + overlayfs.

   > ubirmvol /dev/ubi0 --name=avm_filesys_0
   > ubirmvol /dev/ubi0 --name=avm_filesys_1

8. Flash OpenWRT peristently using sysupgrade.

   > sysupgrade -n /path/to/openwrt-sysupgrade.bin

Signed-off-by: David Bauer <mail@david-bauer.net>