drm/bridge: ite-it6505: add missing Kconfig option select

The IT6505 is using functions provided by the DRM_DP_HELPER driver.
In order to avoid having the bridge enabled but the helper disabled,
let's add a select in order to be sure that the DP helper functions are
always available.

Fixes: b5c84a9e ("drm/bridge: add it6505 driver")
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220426141536.274727-1-fparent@baylibre.com

drivers/gpu/drm/bridge/Kconfig

@@ -78,6 +78,7 @@ config DRM_ITE_IT6505
         tristate "ITE IT6505 DisplayPort bridge"
         depends on OF
         select DRM_KMS_HELPER
+        select DRM_DP_HELPER
         select EXTCON
         help
           ITE IT6505 DisplayPort bridge chip driver.