tests: cover PMU group authorization across exec

[afscoelho_gmail.com]

Summary

Add a credential-changing helper and deterministic ATF cases for inherited resident and evicted groups. Verify that exec reauthorizes authoritative group targets, rejects stale handles with ESRCH, and releases all tracked objects.

Sponsored by: AMD

Signed-off-by: Andre Silva <[e-mail]>

[afscoelho_gmail.com]

Rebase onto main after D58256 landed. main now has its own pmc_exec_test.c, so rename this test to pmc_group_exec_test.c. The test still expects the groups to be dropped, because the owner (nobody) is not privileged.