drm/amd/display: Fix SubVP way calculation

[Why and How]
- Don't skip bottom and next odm pipe when calculating
  num ways for subvp
- Don't need to double cache lines for DCC (divide by 256)

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>