lz4: Add ptest support

lz4: Add ptest support

Add a ptest for lz4.
- It is taking around 9 min to execute with kvm, so added it to PTEST_SLOW.
- It contains one case: test_frame.
- Below is the run log:
  START: ptest-runner
  2023-04-06T00:36
  BEGIN: /usr/lib/lz4/ptest
  Starting lz4frame tester (64-bits, 1.9.4)
  Seed = 7314
  Basic tests completed
  All tests completed
  PASS: lz4/test_frame
  DURATION: 573
  END: /usr/lib/lz4/ptest
  2023-04-06T00:45
  STOP: ptest-runner
  TOTAL: 1 FAIL: 0

Signed-off-by: Qiu Tingting <qiutt@fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>