Subject: [PATCH] Pass MACHINE_ARCH on command line for MIPS kernels.

While there, make param.h guess proper MACHINE_ARCH on hardfloat targets
correctly as well, so tools like bmake can get their defaults right.
This does not help the kernel case, since we compile them with forced
-msoft-float and need to override an incorrect guess by param.h.

Reviewed by: br
Differential Revision: https://reviews.freebsd.org/D8574