drm/amd/display: Disable dmcu fw loading for dcn314

[Why]
DCN 3.1.4 uses dmub not dmcu. Attempt to identify
dmcu firmware for dcn314 results in dm init error:
"Unsupported ASIC type"

[How]
Add dcn314 to the list of asics that don't require dmcu

Signed-off-by: Roman Li <roman.li@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>