configured into the kernel, or when the platform is not supported.
Use the defopt'ed options, rather than NDEC_... and remove the needs-flag
hack that's existed for a while.
Also, put the cpu_decl()s in cpuconf.h, so that platform support files
can pull in the prototypes from there, and pull in options for those
systems for which there is code in the source tree.
deleting (and cleaning up) N pages of #ifdefs in machdep.c. While we're
at it, make the cpu type options generate flags, and check them instead of
kernel Makefile defines.
