s390/ism: add device driver for internal shared memory

Add support for the Internal Shared Memory vPCI Adapter.
This driver implements the interfaces of the SMC-D protocol.

Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>