s390/dasd: Put sub-order definitions in a separate section

There are orders and sub-orders. Put them in different sections for a
better overview.

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>