OMAP: DSS2: Taal: Implement ULPS functionality

ULPS is a low power state where the DSI lanes are kept at ground. This
patch implements ULPS by having a DSI bus inactivity timer which
triggers the entry to ULPS. ULPS exit will happen automatically when the
driver needs to do something on the DSI lanes.

The ulps_timeout is configurable from board file or via sysfs.
Additionally another sysfs file, "ulps", can be used to check the
current ULPS state, or to manually enter or exit ULPS.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

include/video/omap-panel-nokia-dsi.h

@@ -9,6 +9,7 @@ struct omap_dss_device;
  * @use_ext_te: use external TE
  * @ext_te_gpio: external TE GPIO
  * @esd_interval: interval of ESD checks, 0 = disabled (ms)
+ * @ulps_timeout: time to wait before entering ULPS, 0 = disabled (ms)
  * @max_backlight_level: maximum backlight level
  * @set_backlight: pointer to backlight set function
  * @get_backlight: pointer to backlight get function
@@ -22,6 +23,7 @@ struct nokia_dsi_panel_data {
 	int ext_te_gpio;
 
 	unsigned esd_interval;
+	unsigned ulps_timeout;
 
 	int max_backlight_level;
 	int (*set_backlight)(struct omap_dss_device *dssdev, int level);