drm/amd/display: Add option to defer works of hpd_rx_irq

[Why & How]
Due to some code flow constraints, we need to defer dc_lock needed works
from dc_link_handle_hpd_rx_irq(). Thus, do following changes:

* Change allow_hpd_rx_irq() from static to public
* Change handle_automated_test() from static to public
* Extract link lost handling flow out from dc_link_handle_hpd_rx_irq()
  and put those into a new function dc_link_dp_handle_link_loss()
* Add one option parameter to decide whether defer works within
  dc_link_handle_hpd_rx_irq()

Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>