Revert "Revert "drm/amdgpu/display: change pipe policy for DCN 2.0""

This reverts commit 27dd79c0.

It appears MPC_SPLIT_DYNAMIC still causes problems with multiple
displays on DCN2.0 hardware.  Switch back to MPC_SPLIT_AVOID_MULT_DISP.
This increases power usage with multiple displays, but avoids hangs.

Link: drm/amd#2475


Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>