ARM: debug: stm32: add UART early console configuration for STM32F7

Early console is hardcoded on USART1 in current implementation.
With this patch, default UART instance is USART1, but other UART instances
can be configured by setting physical and virtual base addresses in
menuconfig.
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/Kconfig.debug

@@ -1213,12 +1213,13 @@ choice
 
 	config STM32F7_DEBUG_UART
 		bool "Use STM32F7 UART for low-level debug"
-		depends on ARCH_STM32
+		depends on MACH_STM32F746 || MACH_STM32F769
 		select DEBUG_STM32_UART
 		help
 		  Say Y here if you want kernel low-level debugging support
 		  on STM32F7 based platforms, which default UART is wired on
-		  USART1.
+		  USART1, but another UART instance can be selected by modifying
+		  CONFIG_DEBUG_UART_PHYS.
 
 		  If unsure, say N.
 
@@ -1620,7 +1621,7 @@ config DEBUG_UART_PHYS
 	default 0x3e000000 if DEBUG_BCM_KONA_UART
 	default 0x3f201000 if DEBUG_BCM2836
 	default 0x4000e400 if DEBUG_LL_UART_EFM32
-	default 0x40011000 if STM32F4_DEBUG_UART
+	default 0x40011000 if STM32F4_DEBUG_UART || STM32F7_DEBUG_UART
 	default 0x40028000 if DEBUG_AT91_SAMV7_USART1
 	default 0x40081000 if DEBUG_LPC18XX_UART0
 	default 0x40090000 if DEBUG_LPC32XX