UPSTREAM: mm: get rid of unnecessary overhead of trace_mm_page_alloc_extfrag()

(cherry pick from commit 52c8f6a5aeb0bdd396849ecaa72d96f8175528f5)

In general, every tracepoint should be zero overhead if it is disabled.
However, trace_mm_page_alloc_extfrag() is one of exception.  It evaluate
"new_type == start_migratetype" even if tracepoint is disabled.

However, the code can be moved into tracepoint's TP_fast_assign() and
TP_fast_assign exist exactly such purpose.  This patch does it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Bug: 26295735
Bug: 26412925
Bug: 26379045
Change-Id: Ica0bbcc6ca04a4056cc9a07ac7d1185685c4c7c7