[media] V4L: Add camera exposure bias control

The camera may in some conditions incorrectly determine the exposure,
and a manual automatic exposure correction may be needed. This patch
adds V4L2_CID_AUTO_EXPOSURE_BIAS control which allows to add some
offset in the automatic exposure control loop, to compensate for
frame under- or over-exposure.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/media/v4l/controls.xml

@@ -2848,6 +2848,22 @@ remain constant.</entry>
 	  </row>
 	  <row><entry></entry></row>
 
+	  <row>
+	    <entry spanname="id"><constant>V4L2_CID_EXPOSURE_BIAS</constant>&nbsp;</entry>
+	    <entry>integer menu</entry>
+	  </row><row><entry spanname="descr"> Determines the automatic
+exposure compensation, it is effective only when <constant>V4L2_CID_EXPOSURE_AUTO</constant>
+control is set to <constant>AUTO</constant>, <constant>SHUTTER_PRIORITY </constant>
+or <constant>APERTURE_PRIORITY</constant>.
+It is expressed in terms of EV, drivers should interpret the values as 0.001 EV
+units, where the value 1000 stands for +1 EV.
+<para>Increasing the exposure compensation value is equivalent to decreasing
+the exposure value (EV) and will increase the amount of light at the image
+sensor. The camera performs the exposure compensation by adjusting absolute
+exposure time and/or aperture.</para></entry>
+	  </row>
+	  <row><entry></entry></row>
+
 	  <row>
 	    <entry spanname="id"><constant>V4L2_CID_PAN_RELATIVE</constant>&nbsp;</entry>
 	    <entry>integer</entry>