TF-A: create /arm folder and chown to buildslave

There is a temporary need to create softlinks (to be created at
runtime, by CI jobs) on top of /arm folder, these pointing to TOOLS_DIR
folder, so paths at CI scripts' tf_config folder, currently pointing to
/arm are not required to change at this point. Ultimately, the reason
not to change the /arm paths at CI scripts is that Arm CI is running
and cannot be stopped, so once CR01 migration is over and all jobs
running, then Arm CI can fully move to Open CI. One this happens, this
patch can be reverted.

CR01 https://developer.trustedfirmware.org/w/collaboration/openci/

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: Idb9d4a70bb3d134df65cc250cd862dcec87f28d5
1 file changed