fpga: region: move device tree support to of-fpga-region.c

Create of-fpga-region.c and move the following functions without
modification from fpga-region.c.

* of_fpga_region_find
* of_fpga_region_get_mgr
* of_fpga_region_get_bridges
* child_regions_with_firmware
* of_fpga_region_parse_ov
* of_fpga_region_notify_pre_apply
* of_fpga_region_notify_post_remove
* of_fpga_region_notify
* of_fpga_region_probe
* of_fpga_region_remove

Create two new functions with some code from fpga_region_init/exit.

* of_fpga_region_init
* of_fpga_region_exit

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