drm/amdkfd: svm range restore work deadlock when process exit

In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: svm range restore work deadlock when process exit kfd_process_notifier_release flush svm_range_restore_work which calls svm_range_list_lock_and_flush_work to flush deferred_list work, but if deferred_list work mmput release the last user, it will call exit_mmap -> notifier_release, it is deadlock with below backtrace. Move flush svm_range_restore_work to kfd_process_wq_release to avoid deadlock. Then svm_range_restore_work take task->mm ref to avoid mm is gone while validating and mapping ranges to GPU. Workqueue: events svm_range_deferred_list_work [amdgpu] Call Trace: wait_for_completion+0x94/0x100 __flush_work+0x12a/0x1e0 __cancel_work_timer+0x10e/0x190 cancel_delayed_work_sync+0x13/0x20 kfd_process_notifier_release+0x98/0x2a0 [amdgpu] __mmu_notifier_release+0x74/0x1f0 exit_mmap+0x170/0x200 mmput+0x5d/0x130 svm_range_deferred_list_work+0x104/0x230 [amdgpu] process_one_work+0x220/0x3c0