The SoC's pin controller is virtually always built and probed, so
there's is little information to gain from the fact it was successfully
probed. Have the success message show up as debug message to reduce probe
clutter like this:

	NOTICE: stm32-pinctrl soc:pin-controller@50002000.of: pinctrl/gpio driver registered
	NOTICE: stm32-pinctrl soc:pin-controller-z@54004000.of: pinctrl/gpio driver registered

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>