drm/amd/display: reallocate DET for dual displays with high pixel rate ratio

[Why]
For dual displays where pixel rate is much higher on one display,
we may get underflow when DET is evenly allocated.

[How]
Allocate less DET segments for the lower pixel rate display and
more DET segments for the higher pixel rate display

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>