Add a fuzz test for the group syscalls. It drives PMCGROUPCREATE,
PMCGROUPADD, PMCGROUPCOMMIT, and PMCGROUPREAD with random and
out-of-range arguments, in random order, including operations on a
group that does not exist and on one that is already committed.

The kernel must reject every invalid call with an errno and must not
panic. The test takes an iteration count; check-root runs 20000.

Sponsored by: AMD

Signed-off-by: Andre Silva <andasilv@amd.com>