cover-letter: Consolidate the probe_device path

Now that the domain allocation path is less duplicated we can tackle the
probe_device path. Details of this are spread across several functions,
broadly move most of the code into __iommu_probe_device() and organize it
more strictly in terms of paired do/undo functions.

Make the locking simpler by obtaining the group->mutex fewer times and
avoiding adding a half-initialized device to an initialized
group. Previously we would lock/unlock the group three times on these
paths.

Finally we can easily add a properly locked probe_finalize call back so
that modern drivers don't have to use the sketchy unlocked version.

This follows the prior series:

https://lore.kernel.org/r/[email protected]

Cc: Nicolin Chen <[email protected]>
Cc: Lu Baolu <[email protected]>
Cc: Kevin Tian <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>