ARM: dts: sun7i: Add dts file for Bananapi M1 Plus board

Add support for the Bananapi M1 Plus A20 development board from
sinovoip.com.cn . This board is nearly a clone of the Lemaker's
Bananapro, but differ with the wlan chipset connection and i2s pinout.
And I also enable the integrated audio codec on default.

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