drm/amd/display: Clear link res when merging a pipe split

[Description]
- When merging a pipe that was previously pipe split, we need
  to also clear the link resources or the next stream/plane that
  uses the pipe may have an incorrect link resource state

Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>