ARM: dt/sunxi: add NAND controller pin definitions

The pinout is identical to the one on A20 SoCs.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
ARM: sunxi/dt: enable NAND on cubieboard board

Only ONFI timing mode 0 is enabled for now, as it is unclear from the
NAND chip's datasheet whether it can operate reliably with tighter
timings.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>