selftests/damon: split test cases

Currently, the single test program, debugfs.sh, contains all test cases
for DAMON.  When one of the cases fails, finding which case is failed
from the test log is not so easy, and all remaining tests will be
skipped.  To improve the situation, this commit splits the single
program into small test programs having their own names.

Link: https://lkml.kernel.org/r/20211201150440.1088-12-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>