vfio: Refactor vfio_device open and close

This refactor makes the vfio_device_open() to accept device, iommufd_ctx
pointer and kvm pointer. These parameters are generic items in today's
group path and future device cdev path. Caller of vfio_device_open()
should take care the necessary protections. e.g. the current group path
need to hold the group_lock to ensure the iommufd_ctx and kvm pointer are
valid.

This refactor also wraps the group spefcific codes in the device open and
close paths to be paired helpers like:

- vfio_device_group_open/close(): call vfio_device_open/close()
- vfio_device_group_use/unuse_iommu(): this pair is container specific.
				       iommufd vs. container is selected
				       in vfio_device_first_open().

Such helpers are supposed to be moved to group.c. While iommufd related
codes will be kept in the generic helpers since future device cdev path
also need to handle iommufd.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Kevin Tian <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Alex Williamson <[email protected]>
Tested-by: Lixiao Yang <[email protected]>
Tested-by: Yu He <[email protected]>
Signed-off-by: Yi Liu <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

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