drm/msm/dpu: inline _setup_intf_ops()

Inline the _setup_intf_ops() function, it makes it easier to handle
different conditions involving INTF configuration.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/555551/
Link: https://lore.kernel.org/r/20230904020454.2945667-5-dmitry.baryshkov@linaro.org