perf: add perf-scripting feature

perf: add perf-scripting feature

Add a new feature named 'perf-scripting'.  Adding this into the
PERF_FEATURES variable in perf.inc will enable perf scripting on a
target, which will turn on all the language bindings currently
available in perf (Perl and Python), if perf is included in an image.

If 'perf-scripting' isn't named as a feature (the default), all perf
language bindings will be disabled and unavailable.

(From OE-Core rev: fc0661041436013b9099dbd659994a2b8b292c19)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>