mm: introduce per-VMA lock statistics

Add a new CONFIG_PER_VMA_LOCK_STATS config option to dump extra statistics
about handling page fault under VMA lock.

Link: https://lkml.kernel.org/r/20230227173632.3292573-29-surenb@google.com


Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>