device enumeration: Return usb_board_ids as an enum

libhackrf: The usb firmware reports board type as USB product id. Provide hackrf_usb_board_id_name() to decode that.

Do not break hackrf_open() API, provide a hackrf_open_by_serial() instead for the new functionality.

Bug fix, open the correct device in hackrf_device_list_open

hackrf_info: Adjust output to print USB device identification string and device index number, before trying to open.

libhackrf: hackrf_device_list() API for device enumeration and opening of any device (with or without serial numbers).

hackrf_cpldjtag: added -d for device serial number

hackrf_spiflash: added -d for device serial number

Adjust debug printf's a bit

Permit serial number without leading zeros so you don't have to type as much. In fact, permit any suffix of the serial number.