Be consistant in the way that MSIZE, MCLSHIFT, MCLBYTES and NMBCLUSTERS
are defined.
Remove old VM constants from cesfic port.
Bump MSIZE to 256 on mipsco (the only one that wasn't already 256).
MACHINE_ARCH since <arm/param.h> already sets it correctly to "arm".
* For platforms which are not yet ELF, defined MACHINE_ARCH to "arm32"
if __ELF__ is not defined by the C preprocessor.
* In <arm/param.h>, clarify the rules about when MACHINE and
MACHINE_ARCH are defined, and to what. Also, for ELF platforms,
int the non-_KERNEL case, force both MACHINE and MACHINE_ARCH to "arm",
rather than allowing platform-specifc code to define either.