Add support for Radio configuration mode (2/n)

[antoinevg]

This PR depends on #1771 (USB API Bump to 0x0113)

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This PR adds:

• hackrf_open_mode(const enum radio_config_mode mode, hackrf_device** device)
• hackrf_open_mode_by_serial(const char* const desired_serial_number, const enum radio_config_mode mode, hackrf_device** device)
• hackrf_open_device_list_open_mode(hackrf_device_list_t* list, int idx, const enum radio_config_mode mode, hackrf_device** device)
• hackrf_radio_set_mode(hackrf_device* device, const enum radio_config_mode mode)
• ...

TODO

• Reset radio state after mode change
• Compatibility testing
• Get rid of RADIO_LEGACY_MODE
• Don't reload the bitstream if the config mode hasn't changed.
• Return an error when trying to perform an operation not supported by the current config mode.
• Make sure that state reset is working properly (needs Explicit tuning following device reset no longer configures the correct center frequency on pre-release builds. #1785)