perf: change dependencies on python to python3

perf: change dependencies on python to python3

The upstream kernel can now handle python3 for the perf scripts, coupled
with the impending EOL of python2, we switch the dependencies in perf
(scripting) to python3.

Outside of dependency changes, we also pass the following two variables
to the perf build: PYTHON=python3 PYTHON_CONFIG=python3-config. To
ensure that our python3 components are used.

For configurations that disable perf scripting, there is no change in
behaviour.

[YOCTO #13358]

(From OE-Core rev: 584af667e0000129bcb5c9e8108485f2f6590eaf)

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>