sun5i: Add q8_a13_tablet defconfig and dts

This commits adds a generic support for q8 formfactor a13 based tablets.

These tablets ship in many variants, with the difference mainly being the
touchscreen controller / accelerometer / wifi chip used.

The wifi is USB based, and thus not listed in devicetree.

ATM the kernel does not support the touchscreen / accelerometer on these
devices. In the future we may need multiple configs with different
CONFIG_DEFAULT_DEVICE_TREE settings, this depends on how we solve the
hw differences on the kernel side.

For now this will suffice.

The dts files are identical to the dts files submitted to the upstream
kernel for these tablets.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>