simpleperf: fix checking dump regs for tracepoint events.

1. Skip the check for kernel >= 4.2, which already has the patch we
want to test.
2. Use a loop to wait for samples.

Bug: 175075836
Bug: 175174219
Test: run simpleperf_unit_test.
Change-Id: I5e2ae79d2ca82efe722da30285acc192b68eaf3e
4 files changed