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

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/mt8183.rst b/docs/plat/mt8183.rst
index 7a0830f..c639be1 100644
--- a/docs/plat/mt8183.rst
+++ b/docs/plat/mt8183.rst
@@ -17,4 +17,4 @@
 
 .. code:: shell
 
-    make CROSS_COMPILE=aarch64-none-elf- PLAT=mt8183 DEBUG=1
+    make CROSS_COMPILE=aarch64-linux-gnu- PLAT=mt8183 DEBUG=1