drm/amd/display: Correct dram channel width for dcn314

[Why]
The interpretation of the number of memory channels
differ by memory type, and this affects channel width
for the DML input.

[How]
Set dram channel width according to memory type for
dcn314.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Duncan Ma <duncan.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>