ARM: dts: stm32: update uart4 pin configuration for low power on stm32mp157

Sleep pin configuration is refined for low power modes:
- "sleep" (no wakeup & console suspend enabled): put pins in analog state
  to optimize power
- "idle" (wakeup capability): keep Rx pin in alternate function
Signed-off-by: Bich Hemon <bich.hemon@st.com>
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp15-pinctrl.dtsi

@@ -1648,6 +1648,23 @@ pins2 {
 		};
 	};
 
+	uart4_idle_pins_a: uart4-idle-0 {
+		   pins1 {
+			 pinmux = <STM32_PINMUX('G', 11, ANALOG)>; /* UART4_TX */
+		   };
+		   pins2 {
+			 pinmux = <STM32_PINMUX('B', 2, AF8)>; /* UART4_RX */
+			 bias-disable;
+		   };
+	};
+
+	uart4_sleep_pins_a: uart4-sleep-0 {
+		   pins {
+			pinmux = <STM32_PINMUX('G', 11, ANALOG)>, /* UART4_TX */
+				 <STM32_PINMUX('B', 2, ANALOG)>; /* UART4_RX */
+		    };
+	};
+
 	uart4_pins_b: uart4-1 {
 		pins1 {
 			pinmux = <STM32_PINMUX('D', 1, AF8)>; /* UART4_TX */