arm: maxbcm: Enable SPL to include DDR training code into U-Boot

This patch adds SPL support to the maxbcm MV78460 based board. Including
the fixed DDR configuratrion needed for the DDR training code. And the
the serdes PHY init code.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Luka Perkov <luka.perkov@sartura.hr>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 986b4c5..27b38df 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -240,6 +240,7 @@
 config TARGET_MAXBCM
 	bool "Support maxbcm"
 	select CPU_V7
+	select SUPPORT_SPL
 
 config TARGET_DEVKIT3250
 	bool "Support devkit3250"