lantiq: add support for ARV7506PW11 (Alice/O2 IAD 4421)

lantiq: add support for ARV7506PW11 (Alice/O2 IAD 4421)

Ethernet, ADSL2+ and LEDs are fully functional.

Supporting the two TAE ports and SIP gateway was not attempted.

The WiFi is unreliable, due to experimental support for rt35xx family
devices by the rt2800pci driver.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
[rebase to LEDE HEAD]
[switch to normal image instead of brnboot image]
[remove not required pinmux child nodes keys, leds, ebu, exin, pci_in and pci_out]
[remove switch_rst pinmux child node (no support for hw reset in driver/setting a default GPIO value in DT]
[enable usage of the wireless LED]
[fixup mac address configuration]
Sgned-off-by: Mathias Kresin <dev@kresin.me>