lantiq: add support for AVM FRITZ!Box 7430

lantiq: add support for AVM FRITZ!Box 7430

Hardware:
- SoC: Lantiq VRX 220
- CPU: 2x MIPS 34Kc 500 MHz
- RAM: 128 MiB 250 MHz
- Flash: 128 MiB NAND
- Ethernet: Built-in Fast Ethernet switch, 4 ports used
- Wifi: Atheros AR9381-AL1A b/g/n with 2 pcb/internal and 1 external antennas
- USB: 1x USB 2.0
- DSL: Built-in A/VDSL2 modem
- DECT: Dialog SC14441
- LEDs: 1 two-color, 4 one-color
- Buttons: 1x DECT, 1x WIFI
- Telephone connectors: 1 FXS port via TAE or RJ11 connector

With the exception of FXS/DECT everything works
(there are no drivers for AVM's FXS or DECT implementation),
DSL is yet untested.

Installation:
Boot up the device and wait a few seconds. Run the eva_ramboot.py script
in scripts/flashing/ to load the initramfs image on the device:
$ ./scripts/flashing/eva_ramboot.py 192.168.178.1 <path to your initramfs image>
If the script fails to reach the device, maybe try 169.254.120.1.

Wait until booting is complete. You should now be able to reach your device
under the default ip address 192.168.1.1.

Before flashing, check if linux_fs_start is not set to 1 in the tffs partition:
$ fritz_tffs_nand -d /dev/mtd1 -n linux_fs_start
If linux_fs_start is 1, you will need to reset it to 0, either by FTP,
upgrading FritzOS or doing a recovery.

Now you should be able to flash the device using sysupgrade.

Signed-off-by: Leon Maurice Adam <leon.adam@aol.de>
Acked-by: Aleksander Jan Bajkowski <A.Bajkowski@stud.elka.pw.edu.pl>
[drop BOARD_NAME, use wpad-basic-wolfssl, drop 4.19, drop dts-v1,
remove model prefix from LED names]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>