vfio: selftests: Expose more vfio_pci_device functions

vfio: selftests: Expose more vfio_pci_device functions

Refactor and make the functions called under device initialization
public. A later patch adds a test that calls these functions to validate
the UAPI of SR-IOV devices. Opportunistically, to test the success
and failure cases of the UAPI, split the functions dealing with
VFIO_GROUP_GET_DEVICE_FD and VFIO_DEVICE_BIND_IOMMUFD into a core
function and another one that asserts the ioctl. The former will be
used for testing the SR-IOV UAPI, hence only export these.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Vipin Sharma <vipinsh@google.com>
Tested-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20260505212838.1698034-6-rananta@google.com
Signed-off-by: Alex Williamson <alex@shazbot.org>