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.
