sun8i: h2: Add initial Orange Pi R1 support

Orange Pi R1 is an open-source single-board computer using the
Allwinner H2+ SOC.

H2+ Orange Pi R1 has
 - Quad-core Cortex-A7
 - 256MB DDR3
 - micrSD slot
 - 128MBit SPI Nor flash
 - Debug TTL UART
 - 100MBit/s Ethernet (H2+)
 - 100MBit/s Ethernet (RTL8152B)
 - Wifi (RTL8189ETV)
 - USB 2.0 OTG + power supply
This board is very similar to the Orange Pi Zero.

The device tree file is copied from the Linux kernel 4.17.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>