drm/msm/dpu: initialize dpu encoder and connector for writeback

Initialize dpu encoder and connector for writeback if the
target supports it in the catalog.

changes in v2:
	- start initialing the encoder for writeback since we
	have migrated to using drm_writeback_connector_init_with_encoder()
	- instead of checking for WB_2 inside _dpu_kms_initialize_writeback
	call it only when its WB_2
	- rebase on tip of msm-next and remove usage of priv->encoders

changes in v3:
	- none

changes in v4:
	- fix copyright years order

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/483526/
Link: https://lore.kernel.org/r/1650984096-9964-16-git-send-email-quic_abhinavk@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>