Arm backend: Make run.sh run without setup.sh (#10515)

This commit lets the user run run.sh without running setup.sh manually.
As long as the FVP eula has been accepted.

Setup.sh can still be run manually and with another scratchdir set by
the user. But if setup.sh is sourced the scratchdir cannot be set.

Setup.sh has been give some cleanup to handle scratchdir being set by
user and code has been moved into functions.