vfio/platform: return info for device memory mapped IO regions

This patch enables the IOCTLs VFIO_DEVICE_GET_REGION_INFO ioctl call,
which allows the user to learn about the available MMIO resources of
a device.

Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Baptiste Reynal <b.reynal@virtualopensystems.com>
Reviewed-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>