serial: stm32x7: remove stm32f7-usart and stm32h7-usart compatible

This patch remove the extra compatibility string "st,stm32h7-usart"
and "st,stm32f7-usart" to avoid confusion, save some time & space.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>

arch/arm/dts/stm32h743.dtsi

@@ -76,7 +76,7 @@
 		};
 
 		usart1: serial@40011000 {
-			compatible = "st,stm32h7-usart", "st,stm32h7-uart";
+			compatible = "st,stm32h7-uart";
 			reg = <0x40011000 0x400>;
 			interrupts = <37>;
 			status = "disabled";
@@ -84,7 +84,7 @@
 		};
 
 		usart2: serial@40004400 {
-			compatible = "st,stm32h7-usart", "st,stm32h7-uart";
+			compatible = "st,stm32h7-uart";
 			reg = <0x40004400 0x400>;
 			interrupts = <38>;
 			status = "disabled";

drivers/serial/serial_stm32x7.c

@@ -110,9 +110,7 @@ static int stm32_serial_probe(struct udevice *dev)
 
 #if CONFIG_IS_ENABLED(OF_CONTROL)
 static const struct udevice_id stm32_serial_id[] = {
-	{.compatible = "st,stm32f7-usart"},
 	{.compatible = "st,stm32f7-uart"},
-	{.compatible = "st,stm32h7-usart"},
 	{.compatible = "st,stm32h7-uart"},
 	{}
 };