drm/amd/display: Fix prefetch bandwidth calculation for DCN3.1

drm/amd/display: Fix prefetch bandwidth calculation for DCN3.1

[Why]
Prefetch BW calculated is lower than the DML reference because of a
porting error that's excluding cursor and row bandwidth from the
pixel data bandwidth.

[How]
Change the dml_max4 to dml_max3 and include cursor and row bandwidth
in the same calculation as the rest of the pixel data during vactive.

Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Agustin Gutierrez Sanchez <agustin.gutierrez@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>