xtest: stats: dump clock and regulator tree to secure console

Add 'xtest --stats' options '--clocks' and '--regulators' to
respectively dump OP-TEE core clock tree and regulator tree to
the secure console.

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>