rockchip: rk3288: remove fennec board support

Since there is no one using this board, remove it.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index 7d4dc1b..ab3361a 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -28,10 +28,9 @@
 Building
 ========
 
-At present 12 RK3288 boards are supported:
+At present 11 RK3288 boards are supported:
 
    - EVB RK3288 - use evb-rk3288 configuration
-   - Fennec RK3288 - use fennec-rk3288 configuration
    - Firefly RK3288 - use firefly-rk3288 configuration
    - Hisense Chromebook - use chromebook_jerry configuration
    - Asus C100P Chromebook - use chromebook_minnie configuration