drm/amd/display: Add 170Mpix/sec DSC throughput support

[why]
It was missing, although defined in DP spec

[how]
- Add handling of this value to DSC code
- Also remove unused file dsc_helpers.c

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Joshua Aberback <Joshua.Aberback@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>