drm/msm/dpu: separate common function to init physical encoder

Move common DPU physical encoder initialization code to the new function
dpu_encoder_phys_init().

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/540630/
Link: https://lore.kernel.org/r/20230601172236.564445-3-dmitry.baryshkov@linaro.org


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