Add Hummingbird A31 development board

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Update cubieboard2/cubietruck dcdc2/dcdc3 voltages and dvfs data

It has been confirmed that a substantial percentage of cubieboard2
and cubietruck users are having stability issues. These issues are
caused by having various voltages optimistically configured way too
low. Because each unit has its own tolerances, not everyone can
easily reproduce these problems.

To address the issue, we take the updated settings from:
    https://github.com/cubieboard/cubie_configs/tree/09e511721697/sysconfig/linux
This repository is relevant because it is referenced from:
    http://docs.cubieboard.org/tutorials/ct1/development/compiling_latest_kernel_for_cubietruck_cubieboard3
Please note that there is also a sunxi-boards repository fork at
https://github.com/cubieboard (with bad settings) and this makes
things more confusing than necessary.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Adding Merrii A20 Hummingbird support
Merrii_HB:added gmac_power pin