drm/msm/dpu: drop duplicated intf/wb indices from encoder structs

drm/msm/dpu: drop duplicated intf/wb indices from encoder structs

Remove intf_idx and wb_idx fields from struct dpu_encoder_phys and
struct dpu_enc_phys_init_params. Set the hw_intf and hw_wb directly and
use them to get the instance index.

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/540635/
Link: https://lore.kernel.org/r/20230601172236.564445-4-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>