lguest: Fix guest crash when CONFIG_X86_USE_3DNOW=y

One of the very first things lguest_init() does is a memcpy.  On
Athlon/Duron/K7 or CyrixIII/VIA-C3 or Geode GX/LX, this tries to use
MMX.

memcpy -> _mmx_memcpy -> kernel_fpu_begin -> clts -> paravirt_ops.clts

But we haven't set paravirt_ops.clts yet, so we do the native version
and crash.  The simplest solution is to use __memcpy.

Thanks to Michael Rasenberger for the bug report.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>