Clean up initialization of com_regs structure, in preparation for
some additional changers.

Split device_t and softc for all com(4) devices (well, everything that
uses a com_softc backend). Use proper types and ansify where appropriate.

Add an option COM_REGMAP to allow com(4) to use an array of register indices.
This allows us to convert aucom to just another com attachment, and cleanup
some code in the com_arbus.c.

Additionally,

Add an option COM_REGMAP to allow com(4) to use an array of register indices.
This allows us to convert aucom to just another com attachment, and cleanup
some code in the com_arbus.c.

Additionally, we use a common com_cleanup routine rather than having a
zillion copies of it in the attachment points.

This has been tested on a number architectures, and it has been shown to get
close to comparable performance when COM_REGMAP is defined, and comparable
when it is not defined.

Approved by core@. Fixes PR port-evbmips/32362.

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Use device_cfdata().

merge ktrace-lwp.

__KERNEL_RCSID()

Also pass a type argument to comcnattach() and com_kgdb_attach().
comspeed() (and thus cominit()) may need this information.

Use CFATTACH_DECL().

Declare all cfattach structures const.

Added bus probing to avoid bus error.

Deleted verbose error message in probe routine to probe silently.

Renamed sg2com -> com_hpcio. Now it seems to be working on SigmarionII.