Added GPU serial number query and Makefile changes

[vanzod]

I added the query for GPU serial in the main code.
I also modified Makefile to check for nvcc already present in the environment. In this way the user can select the desired CUDA path before make tries to find one available on the default paths.

[AlexanderKomarov]

@vanzod thanks for your pull request. Your decision with searching of nvcc is great.

I have some comments about it:

1. nvmlDeviceGetSerial supported only the Tesla and Quadro products. So I suggest to add validation of card on supporting this function. If no we shouldn't try to get a serial.
2. In your commit "Print PCIe bus IDq" you added duplicate output in 244 lines. Please check it.
3. Why did you added the new library path to Makefile? May be it's your specific path.
4. And there are a problems with indentations.