s390/nvme: support firmware-assisted dump to NVMe disks

From the kernel perspective NVMe dump works exactly like zFCP dump.
Therefore, adapt all places where code explicitly tests only for
IPL of type FCP DUMP. And also set the memory end correctly in this case.

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>