drm/amd/display: Update de-tile override to anticipate pipe splitting

drm/amd/display: Update de-tile override to anticipate pipe splitting

[Why]
For certain MPO configurations, DML will split a pipe after DET buffer has
already been allocated by driver, resulting in allocation of more DET
segments than the configurable return buffer has, causing underflow.

[How]
Determine during DET override calculation whether or not a pipe will be
split later on by DML, and distribute DET segments based on expected
number of pipes.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Taimur Hassan <Syed.Hassan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>