[why]
As hardware team suggested that we need to add a max dsc bw overhead
into existing stream bandwidth when DSC is used.
The formula as below:

max_dsc_bw_overhead =
v_addressable * slice_count * 256 bit * pixel clock / v_total / h_total

effective stream bandwidth = pixel clock * bpp

stream bandwidth = effective stream bandwidth + dsc stream overhead
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@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>