drm/msm/dpu: merge dpu_encoder_init() and dpu_encoder_setup()

drm/msm/dpu: merge dpu_encoder_init() and dpu_encoder_setup()

There is no reason to split the dpu_encoder interface into separate
_init() and _setup() phases. Merge them into a single function.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Abhinav Kumar <quic_abhinavk@quicinc.com> # sc7280
Patchwork: https://patchwork.freedesktop.org/patch/540628/
Link: https://lore.kernel.org/r/20230601172236.564445-2-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>