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/imx8.rst b/docs/plat/imx8.rst
index 49ba374..cec1a39 100644
--- a/docs/plat/imx8.rst
+++ b/docs/plat/imx8.rst
@@ -40,7 +40,7 @@
 
    .. code:: shell
 
-       CROSS_COMPILE=aarch64-linux-gnu- make PLAT=<Target_SoC> bl31
+       CROSS_COMPILE=aarch64-none-elf- make PLAT=<Target_SoC> bl31
 
    Target_SoC should be "imx8qm" for i.MX8QM SoC.
    Target_SoC should be "imx8qx" for i.MX8QX SoC.