drm/amd/display: Re-org and cleanup the redundant code

[Why]
Redundant if-else cases for repeater and non-repeater checks

[How]
Without changing the core logic, rearranged the code by removing
redundant checks

Signed-off-by: Chandan Vurdigere Nataraj <chandan.vurdigerenataraj@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>