Add lyrvpss example driver for the SFFSDR board

Add lyrvpss example driver for the SFFSDR board

Currently there is only a VPFE driver in lyrvpss, and it is called luyrvpfe.
It works with a FPGA bitstream that generates a ramp and sends it over the
VPFE interface. The lyrvpfe driver receives an interrupt each time the HSYNC
line is pulsed (even if the VDINT0 interrupt line is used), and stores and
checks the data to make sure that it is valid. The driver will request a new
frame from the FPGA each time there is a read from /proc/lyrvpfe. For example,
to receive a new frame, issue the following:

  $> cat /proc/lyrvpfe

This will send a request to the FPGA (using the GPIO line) to send a new frame,
wait one second then display the contents of the PING and PONG reception buffers.

Signed-off-by: Hugo Villeneuve <hugo@hugovil.com>