vfree: add debug might_sleep()

Add might_sleep() call to vfree() to catch potential sleep-in-atomic bugs
earlier.

[aryabinin@virtuozzo.com: drop might_sleep_if() from kvfree()]
  Link: http://lkml.kernel.org/r/7e19e4df-b1a6-29bd-9ae7-0266d50bef1d@virtuozzo.com
Link: http://lkml.kernel.org/r/20180914130512.10394-3-aryabinin@virtuozzo.com


Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>