support Radxa Zero

[lafleur]

The Radxa Zero (https://wiki.radxa.com/Zero) is a nanocomputer using the same SOC as the Odroid C2. I took some time to intall archlinuxarm onto it ; I created some needed PKGBUILDs and documented an install process at https://gitlab.com/lafleurdeboum/radxa-zero-pkgbuilds. Feel free to use ; I run this system daily and it didn't fail me.

The most obvious limitation is that there is no support for the hardware video encoder/decoder. I was able to use the GPIO - namely, SPI, UART, I2C - with the vendor-provided kernel and their Device Tree. I suspect it should work with the standard kernel using the vendor's Device Tree, but I didn't try that yet.

Comments very welcome !