ARM: DT: stm32f7: add qspi pin contol node

It also removes the qspi pin configuration done during the
board initialization.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/arch/arm/dts/stm32f746-disco.dts b/arch/arm/dts/stm32f746-disco.dts
index 3d6002f..07e0ca7 100644
--- a/arch/arm/dts/stm32f746-disco.dts
+++ b/arch/arm/dts/stm32f746-disco.dts
@@ -93,6 +93,7 @@
 };
 
 &qspi {
+	pinctrl-0 = <&qspi_pins>;
 	status = "okay";
 
 	qflash0: n25q128a {