powerpc/t4rdb: Add SD boot support for T4240RDB board

This patch adds SD boot support for T4240RDB board. SPL
framework is used. PBL initializes the internal RAM and
copies SPL to it. Then SPL initializes DDR using SPD and
copies u-boot from SD card to DDR, finally SPL transfers
control to u-boot.

Signed-off-by: Chunhe Lan <Chunhe.Lan@freescale.com>
[York Sun: Fix T4240RDB_SDCARD_defcofig]
Reviewed-by: York Sun <yorksun@freescale.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 696f227..b70d9e9 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -128,6 +128,7 @@
 
 config TARGET_T4240RDB
 	bool "Support T4240RDB"
+	select SUPPORT_SPL
 
 config TARGET_CONTROLCENTERD
 	bool "Support controlcenterd"