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

This reverts commit de9bf1d8a2de952bfc17cdf7082b41f9c185e54d.

Change-Id: Iebb6297ce290a10ee850bf6a9c71e7eb530b085f
diff --git a/docs/plat/hikey.rst b/docs/plat/hikey.rst
index d7a01a8..372d388 100644
--- a/docs/plat/hikey.rst
+++ b/docs/plat/hikey.rst
@@ -78,7 +78,7 @@
        EDK2_OUTPUT_DIR=${EDK2_DIR}/Build/HiKey/${BUILD_OPTION}_${AARCH64_TOOLCHAIN}
        # Build fastboot for Trusted Firmware-A. It's used for recovery mode.
        cd ${BUILD_PATH}/atf-fastboot
-       CROSS_COMPILE=aarch64-none-elf- make PLAT=hikey DEBUG=1
+       CROSS_COMPILE=aarch64-linux-gnu- make PLAT=hikey DEBUG=1
        # Convert DEBUG/RELEASE to debug/release
        FASTBOOT_BUILD_OPTION=$(echo ${BUILD_OPTION} | tr '[A-Z]' '[a-z]')
        cd ${EDK2_DIR}