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

This reverts commit de9bf1d8.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f

docs/plat/rpi4.rst

@@ -22,7 +22,7 @@ one universal binary (bl31.bin), which can be built with:
 
 .. 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=``,

docs/plat/ti-k3.rst

@@ -27,7 +27,7 @@ TF-A:
 
 .. code:: shell
 
-    make CROSS_COMPILE=aarch64-none-elf- PLAT=k3 SPD=opteed all
+    make CROSS_COMPILE=aarch64-linux-gnu- PLAT=k3 SPD=opteed all
 
 OP-TEE: