mips: Add support for SoM "VoCore2".

Small patch to add support for VoCore/VoCore2 board.

VoCore is open hardware and runs OpenWrt/LEDE.
It has WIFI, USB, UART, 20+ GPIOs but is only one inch square.
It will help you to make a smart house, study embedded system
or even make the tiniest router in the world.

Details about this SoM can be found at "https://vocore.io/v2.html

".

Signed-off-by: Mauro Condarelli <mc5686@mclink.it>
Reviewed-by: Stefan Roese <sr@denx.de>