libftdi1: Update to 1.5.

New in 1.5 - 2020-07-07
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* Implement tc[io]flush methods & deprecate broken purge_buffers methods

  Please check your code for ftdi_usb_purge_rx_buffer(),
  ftdi_usb_purge_tx_buffer() and ftdi_usb_purge_buffers()
  and migrate to the new ftdi_tc[io]flush() methods.

  Old code will continue to function, but you'll get
  a deprecation warning during compilation.

* Add program to test buffer flush (purge) functionality
* Add kernel driver auto attach/detach.
  See new AUTO_DETACH_REATACH_SIO_MODULE option
* Add ftdi_setflowctrl_xonxoff()
* ftdi_eeprom / eeprom handling:
  * Unify handling of all boolean eeprom flags
  * Add device release number support
  * Add channel_a_driver support for type xxR chips
  * Add support for group0 drive levels on x232H chips
  * Fix handling of high_current_drive parameter
  * Fix inverted handling of VCP driver field for TYPE_R chips
  * New --verbose option for eeprom decode operation
* Add example code for async mode
* Add SPDX license identifiers to the core library & ftdi_eeprom
* Various python SWIG wrapper improvements
* Various cmake file improvements
* Fix small bugs in error code paths

(kleink)