drm/amd/display: Add expanded HBlank field to dc_crtc_timing

drm/amd/display: Add expanded HBlank field to dc_crtc_timing

[Why]
For DP HBlank expansion/reduction, the HBlank parameters of the original
EDID timing needs to be notified to the sink in order for the timing to
be reduced back to the original HBlank size.

[How]
Add parameter in dc_crtc_timing to track the increased HBlank.

Reviewed-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>