drm/amd/display: Optimize remove_duplicates() from O(N^2) to O(N)

drm/amd/display: Optimize remove_duplicates() from O(N^2) to O(N)

Replace the previous O(N^2) implementation of remove_duplicates() with
a O(N) version using a fast/slow pointer approach. The new version
keeps only the first occurrence of each element and compacts the array
in place, improving efficiency without changing functionality.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>