mailbox: omap-mailbox: Check for pending msgs only when mbox is exclusive

mailbox: omap-mailbox: Check for pending msgs only when mbox is exclusive

On TI K3 devices, the mailbox resides in the Always-On power domain
(LPSC_main_alwayson) and is shared among multiple processors. The
mailbox is not solely exclusive to Linux.

Currently, the suspend path checks all FIFO queues for pending messages
and blocks suspend if any are present. This behavior is unnecessary for
K3 devices, since some of the FIFOs are used for RTOS<->RTOS
communication and are independent of Linux.

For FIFOs used in Linux<->RTOS communication, any pending message would
trigger an interrupt, which naturally prevents suspend from completing.
Hence, there is no need for the mailbox driver to explicitly check for
pending messages on K3 platforms.

Introduce a device match flag to indicate whether the mailbox instance
is exclusive to Linux, and skip the pending message check for
non-exclusive instances (such as in K3).

Fixes: a49f991e740f ("arm64: dts: ti: k3-am62-verdin: Add missing cfg for TI IPC Firmware")
Closes: https://lore.kernel.org/all/sid7gtg5vay5qgicsl6smnzwg5mnneoa35cempt5ddwjvedaio@hzsgcx6oo74l/
Signed-off-by: Beleswar Padhi <b-padhi@ti.com>
Tested-by: Hiago De Franco <hiago.franco@toradex.com>
Reviewed-by: Andrew Davis <afd@ti.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>