ramips: add support for Rakwireless RAK633

ramips: add support for Rakwireless RAK633

It's OEM module with 2*26 pin header, similar to LinkIt Smart 7688 or
Vocore2.

Specification:

CPU:       MT7628 580 MHz. MIPS 24K
RAM:       64 MB
Flash:     8 MB
WIFI:      802.11n/g/b 20/40 MHz
USB:       1x Port USB 2.0
Ethernet:  5 Port ethernet switch
UART:      2x

Installation: Use the installed uboot Bootloader. Connect a serial cable
to serialport 0. Turn power on.  Choose the option: "Load system code
then write to Flash via TFTP".  Choose the local device IP and the TFTP
server IP and the file name of the system image.  After if the
Bootloader will copy the image to the local flash.

Notes: The I2C Kernel module work not correctly. You can send and
receive data. But the command i2cdetect doesn’t work. FS#845

Signed-off-by: Eike Feldmann <eike.feldmann@outlook.com>
[commit subject and message touches, DTS whitespace fixes, wifi LED
rename, pinctrl fixes, network settings fixes, lan/wmac mac addresses,
removed i2c kernel modules]
Signed-off-by: Petr Štetiar <ynezz@true.cz>