fpga: zynq-fpga: Change fw format to handle bin instead of bit.

This gets rid of the code to strip away the header and byteswap,
as well as the check for the sync word.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Reviewed-by: Josh Cartwright <joshc@ni.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>