optee: ffa: fix sleep in atomic context

The OP-TEE driver registers the function notif_callback() for FF-A
notifications. However, this function is called in an atomic context
leading to errors like this when processing asynchronous notifications:

 | BUG: sleeping function called from invalid context at kernel/locking/mutex.c:258
 | in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 9, name: kworker/0:0
 | preempt_count: 1, expected: 0
 | RCU nest depth: 0, expected: 0
 | CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted 6.14.0-00019-g657536ebe0aa #13
 | Hardware name: linux,dummy-virt (DT)
 | Workqueue: ffa_pcpu_irq_notification notif_pcpu_irq_work_fn
 | Call trace:
 |  show_stack+0x18/0x24 (C)
 |  dump_stack_lvl+0x78/0x90
 |  dump_stack+0x18/0x24
 |  __might_resched+0x114/0x170
 |  __might_sleep+0x48/0x98
 |  mutex_lock+0x24/0x80
 |  optee_get_msg_arg+0x7c/0x21c
 |  simple_call_with_arg+0x50/0xc0
 |  optee_do_bottom_half+0x14/0x20
 |  notif_callback+0x3c/0x48
 |  handle_notif_callbacks+0x9c/0xe0
 |  notif_get_and_handle+0x40/0x88
 |  generic_exec_single+0x80/0xc0
 |  smp_call_function_single+0xfc/0x1a0
 |  notif_pcpu_irq_work_fn+0x2c/0x38
 |  process_one_work+0x14c/0x2b4
 |  worker_thread+0x2e4/0x3e0
 |  kthread+0x13c/0x210
 |  ret_from_fork+0x10/0x20

Fix this by adding work queue to process the notification in a
non-atomic context.

Fixes: d0476a59de06 ("optee: ffa_abi: add asynchronous notifications")
Cc: stable@vger.kernel.org
Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20250602120452.2507084-1-jens.wiklander@linaro.org
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

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