powerpc/pseries: Enable HVPIPE event message interrupt

The hypervisor signals the OS via a Hypervisor Pipe Event external
interrupt when data is available to be received from the pipe.
Then the OS  should call RTAS check-exception and provide the input
Event Mask as defined for the ‘ibm,hvpipe-msg-events’. In response,
check-exception will return an event log containing an Pipe Events
message. This message contains the source ID for which this
message is intended to and the pipe status such as whether the
payload is pending in the hypervisor or pipe to source is closed.

If there is any user space process waiting in the wait_queue for
the payload from this source ID, wake up that process which can
issue read() to obtain payload with ibm,receive-hvpipe-msg RTAS
or close FD if the pipe to source is closed.

The hypervisor has one pipe per partition for all sources and it
will not deliver another hvpipe event message until the partition
reads the payload for the previous hvpipe event. So if the source
ID is not found in the source list, issue the dummy
ibm,receive-hvpipe-msg RTAS so that pipe will not blocked.

Register hvpipe event source interrupt based on entries from
/proc/device-tree//event-sources/ibm,hvpipe-msg-events property.

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/20250909084402.1488456-8-haren@linux.ibm.com