drm/amd/display: Add new DP_SEC registers for programming SDP Line number

[Why]
Add register for programming in new platform

Signed-off-by: Max.Tseng <Max.Tseng@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Wayne Lin <waynelin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>