kernel: programming the FPGA

It programs the application FPGA using a dedicated char device.
On open() it resets the FPGA
On write() it copies the bitstream on the FPGA
On close() it copies the last word[1] on the bitstream and it enables
the application FPGA

In order to be able to program the application FPGA the user must unlock
the flashing procedure by writing 'unlock' in the `lock` sysfs attribute

[1] This hack is necessary does to an FPGA programmer limitation