s390/dasd: remove setting of scheduler from driver

Remove the hard coded scheduler for the DASD device driver to enable
change of the scheduler during runtime. Set recommended deadline
scheduler via additional udev rule.

Signed-off-by: Stefan Haberland <stefan.haberland@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>