drm/panel/lg-sw43408: select CONFIG_DRM_DISPLAY_DP_HELPER

This panel driver uses DSC PPS functions and as such depends on the
DRM_DISPLAY_DP_HELPER. Select this symbol to make required functions
available to the driver.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404200800.kYsRYyli-lkp@intel.com/
Fixes: 069a6c0e

 ("drm: panel: Add LG sw43408 panel driver")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240528-panel-sw43408-fix-v4-1-330b42445bcc@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>