ARM: dts: sun7i: Add Olimex A20-SOM-EVB-eMMC board

With the new rev.E of A20-SOM-EVB, there is option for 16GB eMMC.
Currently used card is KLMAG2GEND, wired to MMC2 slot.

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