bpf: add selftest for stackmap with build_id in NMI context

This new test captures stackmap with build_id with hardware event
PERF_COUNT_HW_CPU_CYCLES.

Because we only support one ips-to-build_id lookup per cpu in NMI
context, stack_amap will not be able to do the lookup in this test.
Therefore, we didn't do compare_stack_ips(), as it will alwasy fail.

urandom_read.c is extended to run configurable cycles so that it can be
caught by the perf event.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>