GCC: Upgrade to version 9.2-2019.12 of toolchain

This toolchain provides multiple cross compilers and are publicly
available on www.developer.arm.com

We thoroughly test TF-A in CI using:
AArch32 bare-metal target (arm-none-eabi)
AArch64 ELF bare-metal target (aarch64-none-elf)

Change-Id: I2360a3ac6705c68dca781b85e9894867df255b3e
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/plat/intel-agilex.rst b/docs/plat/intel-agilex.rst
index ff27b6b..f60bf14 100644
--- a/docs/plat/intel-agilex.rst
+++ b/docs/plat/intel-agilex.rst
@@ -41,7 +41,7 @@
 
 .. code:: bash
 
-       make CROSS_COMPILE=aarch64-linux-gnu- bl2 fip PLAT=agilex
+       make CROSS_COMPILE=aarch64-none-elf- bl2 fip PLAT=agilex
        BL33=PEI.ROM
 
 Install Procedure