selftests/ftrace: Add a basic testcase for snapshot

This testcase is constrived to reproduce a problem that the cpu buffers
become unavailable which is due to 'record_disabled' of array_buffer and
max_buffer being messed up.

Local test result after bugfix:
  # ./ftracetest test.d/00basic/snapshot1.tc
  === Ftrace unit tests ===
  [1] Snapshot and tracing_cpumask        [PASS]
  [2] (instance)  Snapshot and tracing_cpumask    [PASS]

  # of passed:  2
  # of failed:  0
  # of unresolved:  0
  # of untested:  0
  # of unsupported:  0
  # of xfailed:  0
  # of undefined(test bug):  0

Link: https://lkml.kernel.org/r/20230805033816.3284594-3-zhengyejian1@huawei.com

Cc: <mhiramat@kernel.org>
Cc: <vnagarnaik@google.com>
Cc: <shuah@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>