drm: remove I2C_CLASS_DDC support

After removal of the legacy EEPROM driver and I2C_CLASS_DDC support in
olpc_dcon there's no i2c client driver left supporting I2C_CLASS_DDC.
Class-based device auto-detection is a legacy mechanism and shouldn't
be used in new code. So we can remove this class completely now.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>