Update libfx2.

Implement FPGA bitstream downloading.

Use our own VID:PID pair instead of Cypress one (PID provisional). This also adds an EEPROM access API.

Add basic device firmware.

Add libfx2 submodule.

Implement TCK-only shifts

Speed up tests by turning off legacy divisor for most of them.

Implemented "legacy" 5x clock divider.

Implement loopback commands and fix TDO input.

Implement TDO input.