drm/i915/display/vlv_dsi: Move panel_pwr_cycle_delay to next panel-on

Instead of sleeping panel_pwr_cycle_delay ms when turning the panel off,
record the time it is turned off and if necessary wait any (remaining)
time when the panel is turned on again.

Also sleep the remaining time on shutdown, because on reboot the
GOP will immediately turn on the panel again.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210325114823.44922-2-hdegoede@redhat.com