mailbox: zynqmp: Fix IPI isr handling

mailbox: zynqmp: Fix IPI isr handling

Multiple IPI channels are mapped to same interrupt handler.
Current isr implementation handles only one channel per isr.
Fix this behavior by checking isr status bit of all child
mailbox nodes.

Fixes: 4981b82ba2ff ("mailbox: ZynqMP IPI mailbox controller")
Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230311012407.1292118-3-tanmay.shah@amd.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>