drm/bridge: ite-it66121: Move .mode_set logic to .atomic_enable

drm/bridge: ite-it66121: Move .mode_set logic to .atomic_enable

Move the existing .mode_set logic to the .atomic_enable callback. The
former is deprecated and drivers are supposed to use the latter instead.

Also, drop the struct it66121_ctx.connector field because the connector
can be accessed through the atomic state and there is no need to store
it anymore.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patch.msgid.link/20260523-it66121-fix-dvi-mode-v5-v5-2-33b4468162f9@redhat.com
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>