fpga: region: add fpga-region.h header

* Create fpga-region.h.
* Export fpga_region_program_fpga.
* Move struct fpga_region and other things to the header.

This is a step in separating FPGA region common code
from Device Tree support.

Signed-off-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>