fpga: region: change api, add fpga_region_create/free

Add fpga_region_create/free API functions.

Change fpga_region_register to take FPGA region struct as the only
parameter.  Change fpga_region_unregister to return void.

  struct fpga_region *fpga_region_create(struct device *dev,
                        struct fpga_manager *mgr,
                        int (*get_bridges)(struct fpga_region *));
  void fpga_region_free(struct fpga_region *region);
  int fpga_region_register(struct fpga_region *region);
  void fpga_region_unregister(struct fpga_region *region);

Remove groups storage from struct fpga_region, it's not
needed.  Callers can just "region->dev.groups = groups;"
after calling fpga_region_create.

Update the drivers that call fpga_region_register with the new API.

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