drm/msm/dpu: drop unused lm_max_width from RM

No code uses lm_max_width from resource manager, so drop it. Instead of
calculating the lm_max_width, code can use max_mixer_width field from
the hw catalog.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Link: https://lore.kernel.org/r/20220121210618.3482550-2-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>