setup: disable verbose output of setup.sh

'set -x' prints shell commands and their arguments as they are executed
which makes the output of setup.sh too verbose to follow, so disable the
verbose output for end users to capture critical messages more easily.

Signed-off-by: Lijian Zhang <Lijian.Zhang@arm.com>
Reviewed-by: Tianyu Li <tianyu.li@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

Change-Id: Ie5c012e88603d4989fa46e4788d32265630e55a0