selftests/bpf: Add tracing prog private stack tests

Some private stack tests are added including:
  - main prog only with stack size greater than BPF_PSTACK_MIN_SIZE.
  - main prog only with stack size smaller than BPF_PSTACK_MIN_SIZE.
  - prog with one subprog having MAX_BPF_STACK stack size and another
    subprog having non-zero small stack size.
  - prog with callback function.
  - prog with exception in main prog or subprog.
  - prog with async callback without nesting
  - prog with async callback with possible nesting

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20241112163927.2224750-1-yonghong.song@linux.dev


Signed-off-by: Alexei Starovoitov <ast@kernel.org>