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

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/rpi4.rst b/docs/plat/rpi4.rst
index e87aef7..0f529c1 100644
--- a/docs/plat/rpi4.rst
+++ b/docs/plat/rpi4.rst
@@ -22,7 +22,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-none-elf- make PLAT=rpi4 DEBUG=1
+    CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi4 DEBUG=1
 
 Copy the generated build/rpi4/debug/bl31.bin to the SD card, either
 renaming it to ``armstub8.bin`` or adding an entry starting with ``armstub=``,