ARM: at91: fix Kconfig.debug by adding DEBUG_AT91_UART option

The DEBUG_AT91_UART Kconfig option was forgotten when moving the
AT91 debug-macro.S file. Add it and use it for the at91.S compilation.
Reported-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/Kconfig.debug

@@ -117,16 +117,19 @@ choice
 	config AT91_DEBUG_LL_DBGU0
 		bool "Kernel low-level debugging on rm9200, 9260/9g20, 9261/9g10, 9rl, 9x5, 9n12"
 		select DEBUG_AT91_UART
+		depends on ARCH_AT91
 		depends on HAVE_AT91_DBGU0
 
 	config AT91_DEBUG_LL_DBGU1
 		bool "Kernel low-level debugging on 9263, 9g45 and sama5d3"
 		select DEBUG_AT91_UART
+		depends on ARCH_AT91
 		depends on HAVE_AT91_DBGU1
 
 	config AT91_DEBUG_LL_DBGU2
 		bool "Kernel low-level debugging on sama5d4"
 		select DEBUG_AT91_UART
+		depends on ARCH_AT91
 		depends on HAVE_AT91_DBGU2
 
 	config DEBUG_BCM2835
@@ -1112,6 +1115,10 @@ choice
 
 endchoice
 
+config DEBUG_AT91_UART
+	bool
+	depends on ARCH_AT91
+
 config DEBUG_EXYNOS_UART
 	bool
 
@@ -1168,8 +1175,7 @@ config DEBUG_LL_INCLUDE
 	string
 	default "debug/sa1100.S" if DEBUG_SA1100
 	default "debug/8250.S" if DEBUG_LL_UART_8250 || DEBUG_UART_8250
-	default "debug/at91.S" if AT91_DEBUG_LL_DBGU0 || AT91_DEBUG_LL_DBGU1 || \
-				AT91_DEBUG_LL_DBGU2
+	default "debug/at91.S" if DEBUG_AT91_UART
 	default "debug/asm9260.S" if DEBUG_ASM9260_UART
 	default "debug/clps711x.S" if DEBUG_CLPS711X_UART1 || DEBUG_CLPS711X_UART2
 	default "debug/meson.S" if DEBUG_MESON_UARTAO