docs: GCC toolchain upgrade to version 9.2-2019.12

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

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

Change-Id: I910200174d5bad985504d1af4a1ae5819b524003
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/getting_started/initial-build.rst b/docs/getting_started/initial-build.rst
index 41cd4d1..893aba2 100644
--- a/docs/getting_started/initial-build.rst
+++ b/docs/getting_started/initial-build.rst
@@ -8,13 +8,13 @@
 
    .. code:: shell
 
-       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-
+       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-none-elf-
 
    For AArch32:
 
    .. code:: shell
 
-       export CROSS_COMPILE=<path-to-aarch32-gcc>/bin/arm-eabi-
+       export CROSS_COMPILE=<path-to-aarch32-gcc>/bin/arm-none-eabi-
 
    It is possible to build TF-A using Clang or Arm Compiler 6. To do so
    ``CC`` needs to point to the clang or armclang binary, which will
@@ -32,7 +32,7 @@
 
    .. code:: shell
 
-       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-
+       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-none-elf-
        make CC=<path-to-armclang>/bin/armclang PLAT=<platform> all
 
    Clang will be selected when the base name of the path assigned to ``CC``
@@ -43,7 +43,7 @@
 
    .. code:: shell
 
-       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-
+       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-none-elf-
        make CC=<path-to-clang>/bin/clang PLAT=<platform> all
 
 -  Change to the root directory of the TF-A source tree and build.