perf test shell: Move vfs_getname probe function to lib

perf test shell: Move vfs_getname probe function to lib

Multiple tests will be able to reuse these functions, to test things
like perf report, 'trace', etc, using this probe.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-48xagvozhouhyi8fjota6o2d@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>