drm/atomic: Remove state argument to drm_atomic_private_obj_init

drm/atomic: Remove state argument to drm_atomic_private_obj_init

Now that all drm_private_objs users have been converted to use
atomic_create_state instead of the old ad-hoc initialization, we can
remove the state parameter from drm_private_obj_init and the fallback
code.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260224-drm-private-obj-reset-v5-4-5a72f8ec9934@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>