[media] DocBook/dvb: Use generic descriptions for the frontend API

Move generic stuff into gen-errors.xml, and remove them from
DVB API. While here, removes two bogus error codes that aren't
supported or used on Linux: EINTERNAL and ENOSIGNAL.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/media/v4l/gen-errors.xml

@@ -8,7 +8,7 @@
 	<!-- Keep it ordered alphabetically -->
       <row>
 	<entry>EBADF</entry>
-	<entry><parameter>fd</parameter> is not a valid open file descriptor.</entry>
+	<entry>The file descriptor is not a valid.</entry>
       </row>
       <row>
 	<entry>EBUSY</entry>
@@ -21,18 +21,21 @@
       </row>
       <row>
 	<entry>EFAULT</entry>
-	<entry><parameter>fd</parameter> is not a valid open file descriptor.</entry>
+	<entry>There was a failure while copying data from/to userspace,
+	       probably caused by an invalid pointer reference.</entry>
       </row>
       <row>
 	<entry>EINVAL</entry>
-	<entry>One or more of the ioctl parameters are invalid. This is a widely
-	       used error code. See the individual ioctl requests for actual causes.</entry>
+	<entry>One or more of the ioctl parameters are invalid or out of the
+	       allowed range. This is a widely used error code. See the individual
+	       ioctl requests for specific causes.</entry>
       </row>
       <row>
 	<entry>EINVAL or ENOTTY</entry>
 	<entry>The ioctl is not supported by the driver, actually meaning that
 	       the required functionality is not available, or the file
-	       descriptor is not for a media device.</entry>
+	       descriptor is not for a media device. The usage of EINVAL is
+	       deprecated and will be fixed on a latter patch.</entry>
       </row>
       <row>
         <entry>ENODEV</entry>
@@ -48,6 +51,17 @@
 	       that this request would overcommit the usb bandwidth reserved
 	       for periodic transfers (up to 80% of the USB bandwidth).</entry>
       </row>
+      <row>
+	<entry>ENOSYS or EOPNOTSUPP</entry>
+	<entry>Function not available for this device (dvb API only. Will likely
+	       be replaced anytime soon by ENOTTY).</entry>
+      </row>
+      <row>
+	<entry>EPERM</entry>
+	<entry>Permission denied. Can be returned if the device needs write
+		permission, or some special capabilities is needed
+		(e. g. root)</entry>
+      </row>
       <row>
 	<entry>EWOULDBLOCK</entry>
 	<entry>Operation would block. Used when the ioctl would need to wait