fixes for gpu module:

- fixed printCudaDeviceInfo for new CC
- fixed some compilation errors and warnings
- removed unset command from CMake script
- removed unused std imports

samples/gpu/driver_api_multi.cpp

@@ -54,14 +54,8 @@ inline void safeCall_(int code, const char* expr, const char* file, int line)
 // Each GPU is associated with its own context
 CUcontext contexts[2];
 
-int main(int argc, char **argv)
+int main()
 {
-    if (argc > 1)
-    {
-        cout << "CUDA driver API sample\n";
-        return -1;
-    }
-
     int num_devices = getCudaEnabledDeviceCount();
     if (num_devices < 2)
     {