drm/amd/display: handle DP cpirq

[Why]
This is needed for DP as DP can send us info using irq.

[How]
Check if irq bit is set on short pulse and call the
function that handles cpirq in amdgpu_dm_hdcp

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>