sunxi: add support for Merrii Hummingbird A31

sunxi: add support for Merrii Hummingbird A31

Specifications:
 - SoC: Allwinner A31 @ 1GHz
 - DRAM: 1/2Gb DDR3
 - SD-card slot
 - NAND: 8/16Gb MLC
 - Ethernet: 1x 10/100/1000Mbps (RTL8211E)
 - Wireless: Ampak AP6210 (BCM43362)
 - 2x USB2.0
 - 1x mPCIe slot for 4G cards
 - 1x SIM slot
 - HDMI/VGA via simplefb
 - RTC with battery
 - Power via DC12V / 3A

Installation:
Use the standard sunxi installation to an SD-card. NAND is
not supported.

This is to re-add proper support for an older device.

Link: https://openwrt.org/toh/merrii/hummingbird
Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>