ARM: dts: sun6i: Add dts file for MSI Primo81 tablet

The MSI Primo81 is an A31s based tablet, with 1G RAM, 16G NAND,
768x1024 IPS LCD display, mono speaker, 0.3 MP front camera, 2.0 MP
rear camera, 3500 mAh battery, gt911 touchscreen, mma8452 accelerometer
and rtl8188etv usb wifi. Has "power", "volume+" and "volume-" buttons
(both volume buttons are also connected to the UBOOT_SEL pin). The
external connectors are represented by MicroSD slot, MiniHDMI, MicroUSB
OTG and 3.5mm headphone jack.

USB OTG is enabled in host only mode. AXP221 USB power supply and
GPIO support are required for full USB OTG support.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Signed-off-by: Karsten Merker <merker@debian.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>