drm/amd/display: always program DPPDTO unless not safe to lower

drm/amd/display: always program DPPDTO unless not safe to lower

[Why]
We defer clock updates to after pipes have been programmed. In
some instances we use DPPCLK that have been previously set to be
"unused". This results in a brief window of time where underflow
could occur.

[How]
During prepare bandwidth allow rn_update_clocks_update_dpp_dto
to check each instance and compare previous clock to new clock.
If new clock is higher than previous clock, program DPPDTO.

Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>