optee: ffa: fix sleep in atomic context

In the Linux kernel, the following vulnerability has been resolved:

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.