arm64: mvebu: Add support for the Marvell Armada 3700 SoC

The Armada 3700 integrates the following interfaces (not complete list):
- Dual Cortex-A53 ARMv8
- USB 3.0
- SATA 3.0
- PCIe 2.0
- 2 x Gigabit Ethernet 1Gbps / 2.5Gbps
- ...

This patch adds basic support for this ARMv8 based SoC into U-Boot.
Future patches will integrate other device drivers and board support
for the Marvell DB-88F3720 development board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Wilson Ding <dingwei@marvell.com>
Cc: Victor Gu <xigu@marvell.com>
Cc: Hua Jing <jinghua@marvell.com>
Cc: Terry Zhou <bjzhou@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
diff --git a/arch/arm/mach-mvebu/include/mach/cpu.h b/arch/arm/mach-mvebu/include/mach/cpu.h
index cbec876..66f7680 100644
--- a/arch/arm/mach-mvebu/include/mach/cpu.h
+++ b/arch/arm/mach-mvebu/include/mach/cpu.h
@@ -166,5 +166,12 @@
 
 int mvebu_lcd_register_init(struct mvebu_lcd_info *lcd_info);
 
+/*
+ * get_ref_clk
+ *
+ * return: reference clock in MHz (25 or 40)
+ */
+u32 get_ref_clk(void);
+
 #endif /* __ASSEMBLY__ */
 #endif /* _MVEBU_CPU_H */