powerpc/pseries: Enable hvpipe with ibm,set-system-parameter RTAS

The partition uses “Hypervisor Pipe OS Enablement Notification”
system parameter token (value = 64) to enable / disable hvpipe in
the hypervisor. Once hvpipe is enabled, the hypervisor notifies
OS if the payload is pending for that partition from any source.
This system parameter token takes 1 byte length of data with
1 = Enable and 0 = Disable.

Enable hvpipe in the hypervisor with ibm,set-system-parameter
RTAS after registering hvpipe event source interrupt.

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/20250909084402.1488456-9-haren@linux.ibm.com