jammy-amd64-tf-a-build-lts2.10: Use GNU Arm toolchain 12.3.rel1

Per the official docs:
https://trustedfirmware-a.readthedocs.io/en/lts-v2.10.7/getting_started/prerequisites.html#toolchain

Fixes https://linaro.atlassian.net/browse/TFC-661

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I0a7b82f41f423152dc489b847573bb6833c9699f
1 file changed