x86: Add an inlined __copy_from_user_nmi() variant

Add a inlined __ variant of copy_from_user_nmi. The inlined variant allows
the user to:

 - batch the access_ok() check for multiple accesses

 - avoid having a pagefault_disable/enable() on every access if the
   caller already ensures disabled page faults due to its context.

 - get all the optimizations in copy_*_user() for small constant sized
   transfers

It is just a define to __copy_from_user_inatomic().

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1445551641-13379-1-git-send-email-andi@firstfloor.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>