Revert "GCC: Upgrade to version 9.2-2019.12 of toolchain"

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/rockchip.rst b/docs/plat/rockchip.rst
index 2c3c38f..b7c43fb 100644
--- a/docs/plat/rockchip.rst
+++ b/docs/plat/rockchip.rst
@@ -35,7 +35,7 @@
 
 For AARCH64 architectures the build command looks like
 
-    make CROSS_COMPILE=aarch64-none-elf- PLAT=rk3399 bl32
+    make CROSS_COMPILE=aarch64-linux-gnu- PLAT=rk3399 bl32
 
 while AARCH32 needs a slightly different command