drm/amd/display: Force det buf size to 192KB with 3+ streams and upscaling

[WHY]
This workaround resolves underflow caused by incorrect DST_Y_PREFETCH.
Overriding to 192KB DET buf size until the DST_Y_PREFETCH calc is fixed.

Reviewed-by: Eric Yang <Eric.Yang2@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>