Added defconfig for booting Linux on Radxa Rock board

What works:
- Integrated Ethernet 10/100
- USB 2
- HDMI
- Flash
- MicroSD

What doesn't work yet:
- Wifi+BT
- RK1000-S sound (integrated mic, audio out jack, SPDIF)

Not tested:
- Expansion headers
- RTC
RR minor to avoid recurring irq from missing device

Or else dmesg is full of "rda_bt_host_wake_irq." (7 every 2s)