RT #109267. STM32F7-DISCO: use USART6 as console

The following pins are used for console on STM32F7-DISCO:
  TX = PC6 = Arduino D1
  RX = PC7 = Arduino D0

include/configs/stm32f746-discovery.h

@@ -242,15 +242,15 @@
 #define CONFIG_STM32_USART_CONSOLE
 
 /*
- * USART1, TX PB.6, RX PA.10
+ * USART6, TX PC.6, RX PC.7
  */
-#define CONFIG_STM32_USART_PORT	1		/* USART1 */
+#define CONFIG_STM32_USART_PORT	6		/* USART6 */
 
-#define CONFIG_STM32_USART_TX_IO_PORT	1	/* PORTB */
+#define CONFIG_STM32_USART_TX_IO_PORT	2	/* PORTC */
 #define CONFIG_STM32_USART_TX_IO_PIN	6	/* GPIO6 */
 
-#define CONFIG_STM32_USART_RX_IO_PORT	0	/* PORTA */
-#define CONFIG_STM32_USART_RX_IO_PIN	10	/* GPIO10 */
+#define CONFIG_STM32_USART_RX_IO_PORT	2	/* PORTC */
+#define CONFIG_STM32_USART_RX_IO_PIN	7	/* GPIO7 */
 
 #define CONFIG_BAUDRATE			115200
 #define CONFIG_SYS_BAUDRATE_TABLE	{ 9600, 19200, 38400, 57600, 115200 }