- Move prototypes for various functions into out of C files and into
  <machine/md_var.h>.
- Move some CPU-related variables out of i386/i386/identcpu.c to
  initcpu.c to match amd64.
- Move the declaration of has_f00f_hack out of identcpu.c to machdep.c.
- Remove a misleading comment from i386/i386/initcpu.c (locore zeros
  the BSS before it calls identify_cpu()) and remove explicit zero
  assignments to reduce the diff with amd64.
Remove trailing whitespace.