drm/panel: ilitek-ili9882t: Select DRM_DISPLAY_DSC_HELPER

drm/panel: ilitek-ili9882t: Select DRM_DISPLAY_DSC_HELPER

The panel-ilitek-ili9882t driver uses drm_dsc_pps_payload_pack() which
is provided by the DRM_DISPLAY_DSC_HELPER. Add the missing Kconfig
select to fix the following build error:

  ERROR: modpost: "drm_dsc_pps_payload_pack" [drivers/gpu/drm/panel/panel-ilitek-ili9882t.ko] undefined!

Fixes: 65ce1f5834e9 ("drm/panel: ilitek-ili9882t: Switch Tianma TL121BVMS07 to DSC 120Hz mode")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Link: https://patch.msgid.link/20260115125136.64866-1-mcanal@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>