Add mtk_drm_crtc_path enum for each display path.
Instead of using array index of all_drm_priv in mtk_drm_kms_init(),
mtk_drm_crtc_path enum can make code more readable.
Signed-off-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
Reviewed-by: Fei Shao <fshao@xxxxxxxxxxxx>
Reviewed-by: CK Hu <ck.hu@xxxxxxxxxxxx>
Tested-by: Fei Shao <fshao@xxxxxxxxxxxx>