polkit: add (taken from oe-core)

PolKit will be removed from oe-core as it isn't massively applicable in
embedded, isn't used by anything by default anymore, and future upgrades require
the SpiderMonkey JavaScript runtime.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>