serial: stm32x7: align compatible with kernel one

stm32x7.c driver is dedicated for STM32F7.
In kernel, "st,stm32-usart" and "st,stm32-uart" compatible
strings are dedicated for STM32F4.

To keep U-boot and kernel aligned, replace the serial compatible
string from "st,stm32-usart", "st,stm32-uart" to
"st,stm32f7-usart", "st,stm32f7-uart" specific for STM32F7.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Christophe KERELLO <christophe.kerello@st.com>
Reviewed-by: Patrick DELAUNAY <patrick.delaunay@st.com>
Acked-by: Vikas MANOCHA <vikas.manocha@st.com>

arch/arm/dts/stm32f746.dtsi

@@ -90,7 +90,7 @@
 			status = "disabled";
 		};
 		usart1: serial@40011000 {
-			compatible = "st,stm32-usart", "st,stm32-uart";
+			compatible = "st,stm32f7-usart", "st,stm32f7-uart";
 			reg = <0x40011000 0x400>;
 			interrupts = <37>;
 			clocks = <&rcc 0 164>;

drivers/serial/serial_stm32x7.c

@@ -103,8 +103,8 @@ static int stm32_serial_probe(struct udevice *dev)
 
 #if CONFIG_IS_ENABLED(OF_CONTROL)
 static const struct udevice_id stm32_serial_id[] = {
-	{.compatible = "st,stm32-usart"},
-	{.compatible = "st,stm32-uart"},
+	{.compatible = "st,stm32f7-usart"},
+	{.compatible = "st,stm32f7-uart"},
 	{}
 };