mm/damon/core: add number of each enum type values

This commit declares the number of legal values for each DAMON enum types
to make traversals of such DAMON enum types easy and safe.

Link: https://lkml.kernel.org/r/20220228081314.5770-3-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>