drm/panel: hx83121a: select DRM_DISPLAY_DSC_HELPER

drm/panel: hx83121a: select DRM_DISPLAY_DSC_HELPER

Like a number of other panel drivers, this newly merged driver
needs DRM_DISPLAY_DSC_HELPER to be enabled:

arm-linux-gnueabi-ld: drivers/gpu/drm/panel/panel-himax-hx83121a.o: in function `himax_prepare':
panel-himax-hx83121a.c:(.text+0x1024): undefined reference to `drm_dsc_pps_payload_pack'

Fixes: a7c61963b727 ("drm/panel: Add Himax HX83121A panel driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20260413071043.3829868-1-arnd@kernel.org