ARM: dts: sun7i: Add dts file for A20-OLinuXino-MICRO-eMMC

A20-OLinuXino-MICRO has option with onboard eMMC chip. For
now it's only shipped with 4BG chip, but in the future this
may change.

Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>