sched/psi: introduce tracepoints for psi_memstall_{enter, leave}

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8QUNW



--------------------------------

Two tracepoints are added we can easily use other tools
such as ebpf, ftrace, perf to monitor the memstall data
and do some analysis.

The output of these tracepoints is,
      kcompactd0-58      [001] ....   902.709565: psi_memstall_enter: kcompactd
         kswapd0-132     [003] ....   902.709569: psi_memstall_leave: balance_pgdat
      kcompactd0-58      [001] ....   902.775230: psi_memstall_leave: kcompactd
         kswapd0-132     [003] ....  1337.754598: psi_memstall_enter: balance_pgdat
         kswapd0-132     [003] ....  1337.756076: psi_memstall_leave: balance_pgdat
      kcompactd0-58      [003] ....  1337.756213: psi_memstall_enter: kcompactd
      kcompactd0-58      [003] ....  1337.893188: psi_memstall_leave: kcompactd

Signed-off-by: Lu Jialin <lujialin4@huawei.com>