Refactor USB vendor/product to product string to UsbUtil.h.

Also implement reading of /var/lib/usbutils/usb.ids for systems that
have it (e.g. desktop Linux).

src/UsbUtil.h

@@ -0,0 +1,21 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef CS_USBUTIL_H_
+#define CS_USBUTIL_H_
+
+#include "llvm/SmallVector.h"
+#include "llvm/StringRef.h"
+
+namespace cs {
+
+llvm::StringRef GetUsbNameFromId(int vendor, int product,
+                                 llvm::SmallVectorImpl<char>& buf);
+
+}  // namespace cs
+
+#endif  // CS_USBUTIL_H_