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

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/meson-g12a.rst b/docs/plat/meson-g12a.rst
index 8b06cc2..7cd1bf7 100644
--- a/docs/plat/meson-g12a.rst
+++ b/docs/plat/meson-g12a.rst
@@ -17,7 +17,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-none-elf- make DEBUG=1 PLAT=g12a
+    CROSS_COMPILE=aarch64-linux-gnu- make DEBUG=1 PLAT=g12a
 
 This port has been tested on a SEI510 board. After building it, follow the
 instructions in the `gxlimg repository` or `U-Boot repository`_, replacing the