drm/amd/display: Deallocate IRQ handlers on amdgpu_dm_irq_fini

[why]
The amdgpu_dm IRQ handlers are not freed during the IRQ teardown.

[how]
Add function to deallocate IRQ handlers on amdgpu_dm_irq_fini step.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Victor Lu <victorchengchi.lu@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>