rockchip: rename miniarm to tinker board

Miniarm is the internal project code. Now it is officially named Tinker board.
So rename it.

Signed-off-by: Eddie Cai <eddie.cai@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index 43cafc7..186a1a0 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -42,7 +42,7 @@
    - Fennec RK3288 - use fennec-rk3288 configuration
    - Firefly RK3288 - use firefly-rk3288 configuration
    - Hisense Chromebook - use chromebook_jerry configuration
-   - Miniarm RK3288 - use miniarm-rk3288 configuration
+   - Tinker RK3288 - use tinker-rk3288 configuration
    - PopMetal RK3288 - use popmetal-rk3288 configuration
    - Radxa Rock 2 - use rock2 configuration