board: rockchip: Add Sonoff iHost board

board: rockchip: Add Sonoff iHost board

Sonoff iHost is gateway device designed to provide a Smart Home Hub,
it is based on Rockchip RV1126. There is also a version with 2GB RAM
based off the RV1109 dual core SoC however this works with the same
config as the RV1126 for uboot purposes.

Features:
- Rockchip RV1126
- 4GB DDR4
- 8GB eMMC
- microSD slot
- RMII Ethernet PHY
- 1x USB 2.0 Host
- 1x USB 2.0 OTG
- Realtek RTL8723DS WiFi/BT
- EFR32MG21 Silabs Zigbee radio
- Speaker/Microphone

Signed-off-by: Tim Lunn <tim@feathertop.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>