drm: Add drm_connector_init() variant with ddc

Allow passing ddc adapter pointer to the init function. Even if
drm_connector_init() sometime in the future decides to e.g. memset() all
connector fields to zeros, the newly added function ensures that at its
completion the ddc member of connector is correctly set.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3915224ae895240fd0973cf7f06b9d453e4d8520.1564161140.git.andrzej.p@collabora.com