sunxi: Add support for NanoPi M1

sunxi: Add support for NanoPi M1

NanoPi M1 is a board based on Allwinner H3 CPU.

This commit adds the support for this platform with:
   - an include device tree which enables UART, LEDs, GPIO key switch,
   1 USB host ports and the SD-card as a dtsi file.
   - a device tree specific to this board that enables the
   2 additional USB ports
   - a defconfig file for minimal support
   - a section in MAINTAINERS (add myself)

Synchronized with the kernel device tree, from commits:
sun8i-nanopi.dtsi: 85d2913614d9ab899d23b7ab7d22d23cf45bd1de
sun8i-h3-nanopi-m1.dts: 10efbf5f16336b7540ad6a16aa1cb0b26bab033b

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>