rockchip: add basic support for fennec-rk3288 board

Fennec is a RK3288-based development board with 2 USB ports, HDMI,
micro-SD card, audio and WiFi and Gigabit Ethernet. It also includes
on-board 8GB eMMC and 2GB of SDRAM. Expansion connectors provides access
to display pins, I2C, SPI, UART and GPIOs.

Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index c218a8b..1e44917 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -36,12 +36,13 @@
 Building
 ========
 
-At present four RK3288 boards are supported:
+At present five RK3288 boards are supported:
 
    - Firefly RK3288 - use firefly-rk3288 configuration
    - Radxa Rock 2 - use rock2 configuration
    - Hisense Chromebook - use chromebook_jerry configuration
    - EVB RK3288 - use evb-rk3288 configuration
+   - Fennec RK3288 - use fennec-rk3288 configuration
 
 Two RK3036 board are supported: