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/rpi3.rst b/docs/plat/rpi3.rst
index 38c3dfa..5c7b6d5 100644
--- a/docs/plat/rpi3.rst
+++ b/docs/plat/rpi3.rst
@@ -315,7 +315,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi3             \
+    CROSS_COMPILE=aarch64-none-elf- make PLAT=rpi3             \
     RPI3_BL33_IN_AARCH32=1                                      \
     BL33=../rpi3-arm-tf-bootstrap/aarch32/el2-bootstrap.bin
 
@@ -323,7 +323,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi3             \
+    CROSS_COMPILE=aarch64-none-elf- make PLAT=rpi3             \
     BL33=../rpi3-arm-tf-bootstrap/aarch64/el2-bootstrap.bin
 
 However, enabling PSCI support in a 64-bit kernel is really easy. In the
@@ -340,7 +340,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi3             \
+    CROSS_COMPILE=aarch64-none-elf- make PLAT=rpi3             \
     PRELOADED_BL33_BASE=0x02000000                              \
     RPI3_PRELOADED_DTB_BASE=0x01000000                          \
     RPI3_DIRECT_LINUX_BOOT=1
@@ -349,7 +349,7 @@
 
 .. code:: shell
 
-    CROSS_COMPILE=aarch64-linux-gnu- make PLAT=rpi3             \
+    CROSS_COMPILE=aarch64-none-elf- make PLAT=rpi3             \
     PRELOADED_BL33_BASE=0x02000000                              \
     RPI3_PRELOADED_DTB_BASE=0x01000000                          \
     RPI3_DIRECT_LINUX_BOOT=1                                    \