cam: Add support for viewfinder through DRM/KMS

Use the KMSSink class to display the viewfinder stream, if any, through
DRM/KMS. The output connector is selected through the new -D/--display
argument.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/main.cpp

@@ -132,6 +132,12 @@ int CamApp::parseOptions(int argc, char *argv[])
 			 "Capture until interrupted by user or until <count> frames captured",
 			 "capture", ArgumentOptional, "count", false,
 			 OptCamera);
+#ifdef HAVE_KMS
+	parser.addOption(OptDisplay, OptionString,
+			 "Display viewfinder through DRM/KMS on specified connector",
+			 "display", ArgumentOptional, "connector", false,
+			 OptCamera);
+#endif
 	parser.addOption(OptFile, OptionString,
 			 "Write captured frames to disk\n"
 			 "If the file name ends with a '/', it sets the directory in which\n"