MFC 260557,271076,271077,271082,271083,271098:
- Remove spaces from boot messages when we print the CPU ID/Family/Stepping
- Move prototypes for various functions into out of C files and into
  <machine/md_var.h>.
- Reduce diffs between i386 and amd64 initcpu.c and identcpu.c files.
- Move blacklists of broken TSCs out of the printcpuinfo() function
  and into the TSC probe routine.
- Merge the amd64 and i386 identcpu.c into a single x86 implementation.