drm/msm/dpu: rename dpu_encoder_phys_wb_setup_cdp to match its functionality

dpu_encoder_phys_wb_setup_cdp() is not programming the chroma down
prefetch block. Its setting up the display ctl path for writeback.

Hence rename it to dpu_encoder_phys_wb_setup_ctl() to match what its
actually doing.

Fixes: d7d0e73f

 ("drm/msm/dpu: introduce the dpu_encoder_phys_* for writeback")
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/571812/
Link: https://lore.kernel.org/r/20231212205254.12422-3-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>