fpga: region: don't use drvdata in common fpga code

Changes to fpga_region_register function to not set drvdata.

Setting drvdata is fine for DT based devices that will have one region
per platform device.  However PCIe based devices may have multiple
FPGA regions under one PCIe device.  Without these changes, the PCIe
solution has to create an extra device for each child region to hold
drvdata.

Signed-off-by: Alan Tull <atull@kernel.org>
Reported-by: Jiuyue Ma <majiuyue@huawei.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>