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

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/intel-agilex.rst b/docs/plat/intel-agilex.rst
index f60bf14..ff27b6b 100644
--- a/docs/plat/intel-agilex.rst
+++ b/docs/plat/intel-agilex.rst
@@ -41,7 +41,7 @@
 
 .. code:: bash
 
-       make CROSS_COMPILE=aarch64-none-elf- bl2 fip PLAT=agilex
+       make CROSS_COMPILE=aarch64-linux-gnu- bl2 fip PLAT=agilex
        BL33=PEI.ROM
 
 Install Procedure