Reduce clutter in intel_display.c by moving the scanline moving/stopped
wait functions to intel_vblank.[ch].

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3613b8c22e5022ebf61ab942e6bc81b717e8f520.1673873708.git.jani.nikula@intel.com