drm/amd/display: add cyan_skillfish display support

[Why]
add display related cyan_skillfish files in.

makefile controlled by CONFIG_DRM_AMD_DC_DCN201 flag.

v2: squash in clang fixes from Harry, Nathan
v3: squash in missing CONFIG_DRM_AMD_DC check (Alex)

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Jun Lei <jun.lei@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>