drm/amdgpu: Add preempt and restore callbacks to userq funcs

drm/amdgpu: Add preempt and restore callbacks to userq funcs

Add two new function pointers to struct amdgpu_userq_funcs:
- preempt: To handle preemption of user mode queues
- restore: To restore preempted user mode queues

These callbacks will allow the driver to properly manage queue
preemption and restoration when needed, such as during context
switching or priority changes.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>