drm/amdgpu: disable DCN and VCN for Navi14 0x7340/C9 SKU

Navi14 0x7340/C9 SKU has no display and video support, remove them.

Signed-off-by: Flora Cui <flora.cui@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>