vfio/pci: Rename vfio_pci_device to vfio_pci_core_device

vfio/pci: Rename vfio_pci_device to vfio_pci_core_device

This is a preparation patch for separating the vfio_pci driver to a
subsystem driver and a generic pci driver. This patch doesn't change any
logic.

The new vfio_pci_core_device structure will be the main structure of the
core driver and later on vfio_pci_device structure will be the main
structure of the generic vfio_pci driver.

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20210826103912.128972-4-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>