[S390] kernel: Fix dump on panic for DASDs under LPAR.

Currently the ccw method is used to ipl the DASD dump record under LPAR.
This mechanism is not reliable, which can cause dump failures. This fix
now uses the diag 308 ipl method for all machines, which have diag308
subcode 5 and 4 support.

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>