scripts: edtlib/extract_dts_includes.py: Speed up 2x+ with yaml.CLoader

Use the LibYAML-based yaml.CLoader if available instead of yaml.Loader,
which is written in Python and slow. See
https://pyyaml.org/wiki/PyYAMLDocumentation.

This speeds up gen_defines.py from 0.2s to 0.07s on my system, for
-DBOARD=hifive1. It should also make scripts/kconfig/kconfig.py faster,
because it indirectly uses edtlib via
scripts/kconfig/kconfigfunctions.py.

yaml.CLoader seems to be available out of the box when installing with
pip on Ubuntu at least.

Helps with https://github.com/zephyrproject-rtos/zephyr/issues/20104

.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>