drm/radeon: add late_register for connector

The patch is to solve null dereference in 'aux.dev', which is
introduced in recent radeon rework. By having 'late_register',
the connector should be registered after 'drm_dev_register'
automatically, where in before it is the opposite.

Fixes: 90985660 ("drm/radeon: remove load callback from kms_driver")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3665


Tested-by: Hans de Goede <hdegoede@redhat.com>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Wu Hoi Pok <wuhoipok@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>