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/include/asm/arch-armada-xp/cpu.h b/arch/arm/include/asm/arch-armada-xp/cpu.h
index 6b60c21..4341799 100644
--- a/arch/arm/include/asm/arch-armada-xp/cpu.h
+++ b/arch/arm/include/asm/arch-armada-xp/cpu.h
@@ -96,6 +96,9 @@
 	u32 irq_level;
 };
 
+/* Needed for dynamic (board-specific) mbus configuration */
+extern struct mvebu_mbus_state mbus_state;
+
 /*
  * functions
  */