drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c

dpu_encoder_phys_wb is the only user of encoder's atomic_check callback.
Move corresponding checks to drm_writeback_connector's implementation
and drop the dpu_encoder_phys_wb_atomic_check() function.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Tested-by: Paloma Arellano <quic_parellan@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/577524/
Link: https://lore.kernel.org/r/20240208-fd_remove_phys_ops_atomic_mode_set-v4-4-caf5dcd125c0@linaro.org

drm/msm/dpu: add the writeback connector layer

Introduce the dpu_writeback module which serves as the
interface between dpu operations and the drm_writeback.

This module manages the connector related operations for
dpu writeback.

changes in v2:
- start using drm_writeback_connector_init_with_encoder()
- drop unnecessary arguments from dpu_writeback_init()
- rebase on msm-next tip and remove usage of priv->connectors

changes in v3:
- none

changes in v4:
- none

changes in v5:
- store the drm_enc in the dpu_wb_conn to be used while
using dpu_encoder APIs

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/483520/
Link: https://lore.kernel.org/r/1650984096-9964-15-git-send-email-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>