x86: Declare check_efer() before it gets used

This sparse warning:

  arch/x86/mm/init.c:83:16: warning: symbol 'check_efer' was not declared. Should it be static?

triggers because check_efer() is not decalared before using it.
asm/proto.h includes the declaration of check_efer(), so
including asm/proto.h to fix that - this also addresses the
sparse warning.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <1246458263.6940.22.camel@hpdv5.satnam>
Signed-off-by: Ingo Molnar <mingo@elte.hu>