CONFIG_FPGA in past was a bitfield where bits
were use for vendor identification.

This fix should be the part of this commit:
"Improve configuration of FPGA subsystem"
(sha1: 0133502e)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@ti.com>