drm/amd/display: reduce ODM slice count to initial new dc state only when needed

[why]
We need to decrease ODM slice when adding or removing planes because MPO
support takes precedence over dynamic ODM combine. However there is a case where
we remove ODM combine even for ODM combine required timing in the initial new
dc state. This is normally okay because ODM will be added back after we pass DML
bandwidth validation. However since we remove ODM combine in the initial new
state, the previous ODM pipe allocation is lost. This may cause the new plane to
take away the original secondary OPP head pipe that is still required in the new
state.

For a timing that requires ODM 2:1 but optimized with ODM 4:1, if we add an MPO
plane, we will not have enough pipe to preserve ODM 4:1. In this case we should
reduce ODM slice count then try to add the MPO plane again. By reducing, we are
gradually remove 1 ODM slice from right most side one at a time until we have
enough free pipes for the new plane. If we remove ODM combine entirely, we could
use the pipe at ODM slice index 1 as a DPP pipe for the new plane. But ODM slice
1 is still needed as the timing requires ODM 2:1. This transition is not
seamless and user will see corruption on the screen.

[how]
Remove single ODM slice one at time until we have enough pipes for a new plane.
Remove previous logic to always remove ODM combine entirely.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>