Merge patch series "Move group specific code into group.c"

Yi Liu <yi.l.liu@intel.com> says:

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With the introduction of iommufd, VFIO is towarding to provide device
centric uAPI after adapting to iommufd. With this trend, existing VFIO
group infrastructure is optional once VFIO converted to device centric.

This series moves the group specific code out of vfio_main.c, prepares
for compiling group infrastructure out after adding vfio device cdev[2]

[2] https://github.com/yiliu1765/iommufd/tree/wip/vfio_device_cdev
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Link: https://lore.kernel.org/all/20221201145535.589687-1-yi.l.liu@intel.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>