Add a cn_unit and cn_name field to the consdev structure.
Add a cn_unit and cn_name field to the consdev structure.

Most of the actual use of the cn_dev field is merely to get the name,
and most of the actual initializations are bogusly using makedev()
because the probe/attach has not been completed.

Instead we will migrate console drivers to fill in the name and if
the driver needs it: the unit number, thereby avoiding the bogus
calls to makedev().

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