i3c: master: Make hot-join workqueue freezable to block hot-join during suspend

i3c: master: Make hot-join workqueue freezable to block hot-join during suspend

The I3C master workqueue (master->wq) is used to defer work that needs
thread context and the bus maintenance lock, most notably Hot Join
processing (which calls i3c_master_do_daa() to assign dynamic addresses
to newly joined devices).

Currently the workqueue keeps running across system suspend, which can
race with the suspend path:

 - do_daa() may execute after the controller has been suspended,
   issuing bus transactions on a powered-down or otherwise unusable
   controller.
 - New I3C devices can be enumerated and added to the bus mid-suspend,
   registering driver model objects at a point where the I3C subsystem
   and its consumers are not prepared to handle them.

Mark the workqueue WQ_FREEZABLE so its workers are frozen for the
duration of system suspend/hibernate and resumed afterwards. This
naturally defers any pending or newly queued Hot Join work until the
system (and the controller) is fully resumed, closing both races
without adding explicit suspend/resume synchronization in the master
drivers.

Update the kerneldoc for struct i3c_master_controller::wq to reflect
that the workqueue is freezable.

Fixes: 3a379bbcea0af ("i3c: Add core I3C infrastructure")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260608054312.10604-2-adrian.hunter@intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>