FROMLIST: firmware: arm_scmi: mailbox: support P2A channel completion

i.MX95 System Manager firmware is fully interrupt driven. The notification
channel needs completion interrupt to drive its notification queue. Without
completion interrupt, the notification will work abnormal.

- Add an optional unidirectional mailbox channel. If the channel flag has
  INTR set, and the completion interrupt channel is provided, issue the
  mbox message to Platform after the channel is freed.
- Support bidirectional channel completion interrupt.

Signed-off-by: Peng Fan <peng.fan@nxp.com>

Bug: 342554792
Link: https://lore.kernel.org/all/20240510-scmi-notify-v2-2-e994cf14ef86@nxp.com/


Change-Id: I9488205a7dc98d96aa402e374216a915104c86c2
Signed-off-by: Zhipeng Wang <zhipeng.wang_1@nxp.com>