riscv: dts: add fu740 support

Add dts support for fu740. The HiFive Unmatched support is based on
fu740 cpu and drivers in following patch set.

Signed-off-by: Green Wan <green.wan@sifive.com>
[greentime.hu: set fu740 speed to 1.2GHz]
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>

include/dt-bindings/clock/sifive-fu740-prci.h

@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+/*
+ * Copyright (C) 2020-2021 SiFive, Inc.
+ * Wesley Terpstra
+ * Paul Walmsley
+ * Zong Li
+ * Pragnesh Patel
+ */
+
+#ifndef __DT_BINDINGS_CLOCK_SIFIVE_FU740_PRCI_H
+#define __DT_BINDINGS_CLOCK_SIFIVE_FU740_PRCI_H
+
+/* Clock indexes for use by Device Tree data and the PRCI driver */
+
+#define PRCI_CLK_COREPLL	0
+#define PRCI_CLK_DDRPLL		1
+#define PRCI_CLK_GEMGXLPLL	2
+#define PRCI_CLK_DVFSCOREPLL	3
+#define PRCI_CLK_HFPCLKPLL	4
+#define PRCI_CLK_CLTXPLL	5
+#define PRCI_CLK_TLCLK		6
+#define PRCI_CLK_PCLK		7
+#define PRCI_CLK_PCIEAUX	8
+
+#endif