drm/i915/panel: sync panel prepared state at register

If the panel is enabled at probe, and we take over the hardware state,
the drm_panel prepared state will be out of sync. We'll need to notify
drm_panel framework about the state at probe, so it can in turn notify
the panel followers.

Cc: Lee Shawn C <shawn.c.lee@intel.com>
Tested-by: Lee Shawn C <shawn.c.lee@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/a33e4fe5e9970aed9c4aef8c426c00a189149c32.1749199013.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>