s390: nvme dump support

Add the nvme dump ipl type, associated data, and sysfs entries. This allows
booting into a stand alone dump environment that resides on an nvme device.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>