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 <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Michael Petlan <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Thomas Richter <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>