Rather than include a copy for memmove to call bcopy to call memcpy
(which handles overlapping copies), make memmove a strong reference to
memcpy to save the two calls.
Differential Revision: https://reviews.freebsd.org/D15374
riscv and powerpc have nearly identical bcopy.c that's
supposed to be mostly MI. Move it to the MI libkern.
Differential Revision: https://reviews.freebsd.org/D15374