Make some variables and functions static when not used outside of a module.
Make variables in headers extern.
Delete the unused db_find_watchpoint() function.
- replace opt_kgdb_machdep.h with opt_kgdb.h
- defparam opt_kgdb.h:
KGDB_DEV KGDB_DEVNAME KGDB_DEVADDR KGDB_DEVRATE KGDB_DEVMODE
- move from opt_ddbparam.h to opt_ddb.h:
DDB_FROMCONSOLE DDB_ONPANIC DDB_HISTORY_SIZE DDB_BREAK_CHAR SYMTAB_SPACE
- replace KGDBDEV with KGDB_DEV
- replace KGDBADDR with KGDB_DEVADDR
- replace KGDBMODE with KGDB_DEVMODE
- replace KGDBRATE with KGDB_DEVRATE
- use `9600' instead of `0x2580' for 9600 baud rate
- use correct quotes for options KGDB_DEVNAME="\"com\""
- use correct quotes for options KGDB_DEV="17*256+0"
- remove unnecessary dependancy on Makefile for kgdb_stub.o
- minor whitespace cleanup
