Arm: dts: stm32: remove extra compatible string for uart

This patch removes the extra compatibility string "st,stm32-usart" to
avoid confusion, save some time & space.
Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/dma/stm32-dma.txt

@@ -71,7 +71,7 @@ channel: a phandle to the DMA controller plus the following four integer cells:
 Example:
 
 	usart1: serial@40011000 {
-		compatible = "st,stm32-usart", "st,stm32-uart";
+		compatible = "st,stm32-uart";
 		reg = <0x40011000 0x400>;
 		interrupts = <37>;
 		clocks = <&clk_pclk2>;

Documentation/devicetree/bindings/serial/st,stm32-usart.txt

@@ -2,14 +2,10 @@
 
 Required properties:
 - compatible: can be either:
-  - "st,stm32-usart",
   - "st,stm32-uart",
-  - "st,stm32f7-usart",
   - "st,stm32f7-uart",
-  - "st,stm32h7-usart"
   - "st,stm32h7-uart".
-  depending on whether the device supports synchronous mode
-  and is compatible with stm32(f4), stm32f7 or stm32h7.
+  depending is compatible with stm32(f4), stm32f7 or stm32h7.
 - reg: The address and length of the peripheral registers space
 - interrupts:
   - The interrupt line for the USART instance,
@@ -33,7 +29,7 @@ usart4: serial@40004c00 {
 };
 
 usart2: serial@40004400 {
-	compatible = "st,stm32-usart", "st,stm32-uart";
+	compatible = "st,stm32-uart";
 	reg = <0x40004400 0x400>;
 	interrupts = <38>;
 	clocks = <&clk_pclk1>;
@@ -43,7 +39,7 @@ usart2: serial@40004400 {
 };
 
 usart1: serial@40011000 {
-	compatible = "st,stm32-usart", "st,stm32-uart";
+	compatible = "st,stm32-uart";
 	reg = <0x40011000 0x400>;
 	interrupts = <37>;
 	clocks = <&rcc 0 164>;