GenWQE: Use pci_(request|release)_mem_regions

Now that we do have pci_request_mem_regions() and pci_release_mem_regions()
at hand, use it in the genwqe driver.

[bhelgaas: fix build issues]
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
CC: Frank Haverkamp <haver@linux.vnet.ibm.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>