Attempt to make break-to-debugger and alternative break-to-debugger more
accessible:

(1) Always compile in support for breaking into the debugger if options
    KDB is present in the kernel.

(2) Disable both by default, but allow them to be enabled via tunables
    and sysctls debug.kdb.break_to_debugger and
    debug.kdb.alt_break_to_debugger.

(3) options BREAK_TO_DEBUGGER and options ALT_BREAK_TO_DEBUGGER continue
    to behave as before -- only now instead of compiling in
    break-to-debugger support, they change the default values of the
    above sysctls to enable those features by default.  Current kernel
    configurations should, therefore, continue to behave as expected.

(4) Migrate alternative break-to-debugger state machine logic out of
    individual device drivers into centralised KDB code.  This has a
    number of upsides, but also one downside: it's now tricky to release
    sio spin locks when entering the debugger, so we don't.  However,
    similar logic does not exist in other device drivers, including uart.

(5) dcons requires some special handling; unlike other console types, it
    allows overriding KDB's own debugger selection, so we need a new
    interface to KDB to allow that to work.

GENERIC kernels will now support break-to-debugger as long as appropriate
boot/run-time options are set, which should improve the debuggability of
kernels significantly.

MFC: r225214 (partial)

Follow up to r225203 refining break-to-debugger run-time configuration
improvements:

(1) Implement new model in previously missed at91 UART driver
(2) Move BREAK_TO_DEBUGGER and ALT_BREAK_TO_DEBUGGER from opt_comconsole.h
    to opt_kdb.h (spotted by np)
(3) Garbage collect now-unused opt_comconsole.h

o  Properly use rman(9) to manage resources. This eliminates the
   need to puc-specific hacks to rman. It also allows devinfo(8)
   to be used to find out the specific assignment of resources to
   serial/parallel ports.
o  Compress the PCI device "database" by optimizing for the common
   case and to use a procedural interface to handle the exceptions.
   The procedural interface also generalizes the need to setup the
   hardware (program chipsets, program clock frequencies).
o  Eliminate the need for PUC_FASTINTR. Serdev devices are fast by
   default and non-serdev devices are handled by the bus.
o  Use the serdev I/F to collect interrupt status and to handle
   interrupts across ports in priority order.
o  Sync the PCI device configuration to include devices found in
   NetBSD and not yet merged to FreeBSD.
o  Add support for Quatech 2, 4 and 8 port UARTs.
o  Add support for a couple dozen Timedia serial cards as found
   in Linux.

the kernel by wrapping all targets for fake opt_*.h files in
.if defined(KERNBUILDDIR).  Thus, such fake files won't be
created at all if modules are built with the kernel.

Some modules undergo cleanup like removing unused or unneeded
options or .h files, without which they wouldn't build this way
or the other.

Reviewed by:	ru
Tested by:	no binary changes in modules built alone
Tested on:	i386 sparc64 amd64

  - Move MD files into <arch>/<arch>.
  - Move bus dependent files into <arch>/<bus>.
Rename some files to more suitable names.

Repo-copied by:	peter
Discussed with:	imp

o  Add opt_gdb.h and opt_kdb.h to SRCS.

the modules.

Also generate usbdevs.h automatically now, but a non-kernel file is
stopping that at the moment.

- SRCS was totally disordered.
- the echos to create options headers were hidden using '@'.
- the args of echos to create options headers were single-quoted.
- the target names for the rules to create options headers were repeated.
- the unused option COMPAT_FREEBSD4 was put in opt_compat.h.

disordered.  This commit only fixes the external disorder by
rearranging whole lines.