drs: rgb camera hook (#524)

## Link to GitHub Issue, if one exists
n/a

## Description of change
Add plug&play hooks for RGB camera in DRS.

## Testing
Seems to work with my crappy Logitech C270

Camera options (brightness etc) seem to work in test menu as well).

Tested by another user with realsense camera + logitech camera, both
cams were detected correctly.

src/spice2x/CMakeLists.txt

@@ -441,6 +441,7 @@ set(SOURCE_FILES ${SOURCE_FILES}
         games/scotto/io.cpp
         games/drs/drs.cpp
         games/drs/io.cpp
+        games/drs/rgb_cam.cpp
         games/we/we.cpp
         games/we/io.cpp
         games/we/touchpanel.cpp