drm/bridge: Fix it6505 Kconfig DRM_DP_AUX_BUS dependency

it6505 depends on DRM_DP_AUX_BUS, the kconfig for it6505 should
reflect this dependency using 'select'.

Fixes: b5c84a9e

 ("drm/bridge: add it6505 driver")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220421131415.1289469-1-robert.foss@linaro.org