x86: Fix booting with "no387 nofxsr"

Jesper Juhl reported that testing the software math-emulation by forcing
"no387" doesn't work on modern CPU's.

The reason was two-fold:
 - you also need to pass in "nofxsr" to make sure that we not only don't
   touch the old i387 legacy hardware, it also needs to disable the
   modern XMM/FXSR sequences
 - "nofxsr" didn't actually clear the capability bits immediately,
   leaving the early boot sequence still using FXSR until we got to
   the identify_cpu() stage.

This fixes the "nofxsr" flag to take effect immediately on the boot CPU.

Debugging by Randy Dunlap

Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Jesper Juhl <jesper.juhl@gmail.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>