sgi575/run_model: do not overwrite soc uart1 log file name for automated tests

The uefi-mm logs are printed over the soc uart1 port and a log file name
is assigned to it when the model is launched. So do not override that file
name for automated tests with -j parameter.

Change-Id: I81ef205a54a87e72fc850a66115acf4cae4e860b
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>