ARM: mmp: implement DEBUG_LL port choice

DEBUG_LL port must be choiced in arch-mmp. DEBUG_LL port should be
UART2 in TTC DKB. And it should be UART3 in brownstone.

Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index f15f82b..0919191 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -224,6 +224,20 @@
 		  Say Y here if you want kernel low-level debugging support
 		  on i.MX6Q UART4.
 
+	config DEBUG_MMP_UART2
+		bool "Kernel low-level debugging message via MMP UART2"
+		depends on ARCH_MMP
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on MMP UART2.
+
+	config DEBUG_MMP_UART3
+		bool "Kernel low-level debugging message via MMP UART3"
+		depends on ARCH_MMP
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on MMP UART3.
+
 	config DEBUG_MSM_UART1
 		bool "Kernel low-level debugging messages via MSM UART1"
 		depends on ARCH_MSM7X00A || ARCH_MSM7X30 || ARCH_QSD8X50