vfio-pci: Fault mmaps to enable vma tracking

commit 11c4cd07ba111a09f49625f9e4c851d83daf0a22 upstream.

Rather than calling remap_pfn_range() when a region is mmap'd, setup
a vm_ops handler to support dynamic faulting of the range on access.
This allows us to manage a list of vmas actively mapping the area that
we can later use to invalidate those mappings.  The open callback
invalidates the vma range so that all tracking is inserted in the
fault handler and removed in the close handler.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
[Ajay: Regenerated the patch for v4.19]
Signed-off-by: Ajay Kaher <akaher@vmware.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>