[media] v4l: Add AUTO option for the V4L2_CID_POWER_LINE_FREQUENCY control

V4L2_CID_POWER_LINE_FREQUENCY control allows applications to instruct
a driver what is the power line frequency so an appropriate filter
can be used by the device to cancel flicker by compensating the light
intensity ripple. Currently in the menu we have entries for 50 Hz and
60 Hz and for entirely disabling the anti-flicker filter.
However some devices are capable of automatically detecting the
frequency, so add V4L2_CID_POWER_LINE_FREQUENCY_AUTO entry for them.

Signed-off-by: Sylwester Nawrocki <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>
Acked-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/DocBook/media/v4l/controls.xml

···
 	    <entry>Enables a power line frequency filter to avoid
 flicker. Possible values for <constant>enum v4l2_power_line_frequency</constant> are:
 <constant>V4L2_CID_POWER_LINE_FREQUENCY_DISABLED</constant> (0),
-<constant>V4L2_CID_POWER_LINE_FREQUENCY_50HZ</constant> (1) and
-<constant>V4L2_CID_POWER_LINE_FREQUENCY_60HZ</constant> (2).</entry>
+<constant>V4L2_CID_POWER_LINE_FREQUENCY_50HZ</constant> (1),
+<constant>V4L2_CID_POWER_LINE_FREQUENCY_60HZ</constant> (2) and
+<constant>V4L2_CID_POWER_LINE_FREQUENCY_AUTO</constant> (3).</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CID_HUE_AUTO</constant></entry>

drivers/media/video/v4l2-ctrls.c

···
 		"Disabled",
 		"50 Hz",
 		"60 Hz",
+		"Auto",
 		NULL
 	};
 	static const char * const camera_exposure_auto[] = {

include/linux/videodev2.h

···
 	V4L2_CID_POWER_LINE_FREQUENCY_DISABLED	= 0,
 	V4L2_CID_POWER_LINE_FREQUENCY_50HZ	= 1,
 	V4L2_CID_POWER_LINE_FREQUENCY_60HZ	= 2,
+	V4L2_CID_POWER_LINE_FREQUENCY_AUTO	= 3,
 };
 #define V4L2_CID_HUE_AUTO			(V4L2_CID_BASE+25)
 #define V4L2_CID_WHITE_BALANCE_TEMPERATURE	(V4L2_CID_BASE+26)