ARM: dts: stm32: remove useless pinctrl entries in stm32mp157-pinctrl

This patch removes "ngpios" and "gpio-ranges" information from
stm32mp157-pinctrl.dtsi file as it is now filled in stm32mp157 pinctrl
package files.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>