libcamera: stream: Add StillCaptureRaw role

Add a role for capturing high resolution, low frame rate, still images
in RAW format.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/stream.h

@@ -58,6 +58,7 @@ private:
 
 enum StreamRole {
 	StillCapture,
+	StillCaptureRaw,
 	VideoRecording,
 	Viewfinder,
 };