python3: add toggle for profile-guided-optimisation
Add a PACKAGECONFIG for profile-guided-optimisation, and default to whether
qemu-usermode is available.
Move --enable-optimizations to the pgo optimisation as all this currently does
is use the PGO rules, causing a performance hit if PGO isn't actually used.
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>