drm/msm/dp: allow voltage swing / pre emphasis of 3

Both dp_link_adjust_levels() and dp_ctrl_update_vx_px() limit swing and
pre-emphasis to 2, while the real maximum value for the sum of the
voltage swing and pre-emphasis is 3. Fix the DP code to remove this
limitation.

Fixes: c943b494 ("drm/msm/dp: add displayPort driver support")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/577006/
Link: https://lore.kernel.org/r/20240203-dp-swing-3-v1-1-6545e1706196@linaro.org