drm/amd/display: Add DP required HBlank size calc to link interface

drm/amd/display: Add DP required HBlank size calc to link interface

[Why]
Some features, such as HBlank expansion/reduction, needs to know how
much HBlank is required to support basic audio.

[How]
Add interface to link to calculate required HBlank size for a given
link + timing combination to support basic audio (i.e. 2-channel 48KHz).

Reviewed-by: Wenjing Liu <wenjing.liu@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>