sunxi: Add Libre Computer ALL-H3-IT H5 board

The Libre Computer ALL-H3-IT board is a small single board computer that
is roughly the same size as the Raspberry Pi Zero, or around 20% smaller
than a credit card.

The board features:

  - H2, H3, or H5 SoC from Allwinner
  - 2 DDR3 DRAM chips
  - Realtek RTL8821CU based WiFi module
  - 128 Mbit SPI-NOR flash
  - micro-SD card slot
  - micro HDMI video output
  - FPC connector for camera sensor module
  - generic Raspberri-Pi style 40 pin GPIO header
  - additional pin headers for extra USB host ports, ananlog audio and
    IR receiver

Only H5 variant test samples were made available, but the vendor does
have plans to include at least an H3 variant. Thus the device tree is
split much like the ALL-H3-CC, with a common dtsi file for the board
design, and separate dts files including the common board file and the
SoC dtsi file. The other variants will be added as they are made
available.

The device tree was synced over from the Linux kernel, along with other
H3/H5 changes, in a previous patch. Thus only the defconfig and an entry
to the MAINTAINERS file is added.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
[jagan: drop CONFIG_SYS_SPI_U_BOOT_OFFS]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>