drm/amd/display: Always update divider settings for DP tunnel

drm/amd/display: Always update divider settings for DP tunnel

[Why]
When transitioning from 640x480 at RBRx1 to HBR3x1,
both output pixel mode and pixel rate divider should update.
The needs_divider_update flag was only for 8b10b and 128b132b transition.

[How]
For DP tunneling, always update divider settings.

Reviewed-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Cruise Hung <Cruise.Hung@amd.com>
Signed-off-by: Matthew Stewart <matthew.stewart2@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>