net/smc: manage system EID in SMC stack instead of ISM driver

The System EID (SEID) is an internal EID that is used by the SMCv2
software stack that has a predefined and constant value representing
the s390 physical machine that the OS is executing on. So it should
be managed by SMC stack instead of ISM driver and be consistent for
all ISMv2 device (including virtual ISM devices) on s390 architecture.

Suggested-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Reviewed-and-tested-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>