powerpc/pseries: HVPIPE changes to support migration

The hypervisor assigns one pipe per partition for all sources and
assigns new pipe after migration. Also the partition ID that is
used by source as its target ID may be changed after the migration.
So disable hvpipe during SUSPEND event with ‘hvpipe enable’ system
parameter value = 0 and enable it after migration during RESUME
event with  hvpipe enable’ system parameter value = 1.

The user space calls such as ioctl()/ read() / write() / poll()
returns  -ENXIO between SUSPEND and RESUME events. The user space
process can close FD and reestablish connection with new FD after
migration if needed (Example: source IDs are changed).

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Tested-by: Shashank MS <shashank.gowda@in.ibm.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250909084402.1488456-10-haren@linux.ibm.com