drm/i915/display/vlv_dsi: Do not skip panel_pwr_cycle_delay when disabling the panel

After the recently added commit fe0f1e3b ("drm/i915: Shut down
displays gracefully on reboot"), the DSI panel on a Cherry Trail based
Predia Basic tablet would no longer properly light up after reboot.

I've managed to reproduce this without rebooting by doing:
chvt 3; echo 1 > /sys/class/graphics/fb0/blank;\
echo 0 > /sys/class/graphics/fb0/blank

Which rapidly turns the panel off and back on again.

The vlv_dsi.c code uses an intel_dsi_msleep() helper for the various delays
used for panel on/off, since starting with MIPI-sequences version >= 3 the
delays are already included inside the MIPI-sequences.

The problems exposed by the "Shut down displays gracefully on reboot"
change, show that using this helper for the panel_pwr_cycle_delay is
not the right thing to do. This has not been noticed until now because
normally the panel never is cycled off and directly on again in quick
succession.

Change the msleep for the panel_pwr_cycle_delay to a normal msleep()
call to avoid the panel staying black after a quick off + on cycle.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Fixes: fe0f1e3b ("drm/i915: Shut down displays gracefully on reboot")
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/20210325114823.44922-1-hdegoede@redhat.com

drivers/gpu/drm/i915/display/vlv_dsi.c

@@ -993,14 +993,14 @@ static void intel_dsi_post_disable(struct intel_atomic_state *state,
 	 * FIXME As we do with eDP, just make a note of the time here
 	 * and perform the wait before the next panel power on.
 	 */
-	intel_dsi_msleep(intel_dsi, intel_dsi->panel_pwr_cycle_delay);
+	msleep(intel_dsi->panel_pwr_cycle_delay);
 }
 
 static void intel_dsi_shutdown(struct intel_encoder *encoder)
 {
 	struct intel_dsi *intel_dsi = enc_to_intel_dsi(encoder);
 
-	intel_dsi_msleep(intel_dsi, intel_dsi->panel_pwr_cycle_delay);
+	msleep(intel_dsi->panel_pwr_cycle_delay);
 }
 
 static bool intel_dsi_get_hw_state(struct intel_encoder *encoder,