s390/zcrypt: Rework ap init in case of out of range domain param.

When a out of range domain parameter was given, the init function
returned with -EINVAL and the driver was not operational. As the
driver is statically build into the kernel and is able to work
with multiple domains anyway the init function should continue.
Now the user has a chance to write a new default domain value
via sysfs attribute file. Also added two new dbf debug messages
related to the domain value handling.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>