CI: use external-arm-toolchain 10.3

The 11.2 release of the Arm GCC uses Broadwell-onwards instructions, but
our CI (and many other users) have pre-Broadwell hardware.

Until 11.3 is released which fixes this, go back to using 10.3 for our CI.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/get-binary-toolchains

@@ -2,7 +2,7 @@
 set -u
 
 HOST_ARCH=$(uname -m)
-VER="11.2-2022.02"
+VER="10.3-2021.07"
 
 DOWNLOAD_DIR=$1
 TOOLCHAIN_DIR=$2