s390/ism: Consolidate SMC-D-related code

The ism module had SMC-D-specific code sprinkled across the entire module.
We are now consolidating the SMC-D-specific parts into the latter parts
of the module, so it becomes more clear what code is intended for use with
ISM, and which parts are glue code for usage in the context of SMC-D.
This is the fourth part of a bigger overhaul of the interfaces between SMC
and ISM.

Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Jan Karcher <jaka@linux.ibm.com>
Signed-off-by: Wenjia Zhang <wenjia@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>