riscv: Add a SYSCON driver for SiFive's Core Local Interruptor

This adds U-Boot syscon driver for SiFive's Core Local Interruptor
(CLINT). The CLINT block holds memory-mapped control and status
registers associated with software and timer interrupts.

This driver implements the riscv_get_time() API as required by
the generic RISC-V timer driver, as well as some other APIs that
are needed for handling IPI.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
diff --git a/arch/riscv/include/asm/global_data.h b/arch/riscv/include/asm/global_data.h
index 4d5d623..46fcfab 100644
--- a/arch/riscv/include/asm/global_data.h
+++ b/arch/riscv/include/asm/global_data.h
@@ -12,6 +12,9 @@
 
 /* Architecture-specific global data */
 struct arch_global_data {
+#ifdef CONFIG_SIFIVE_CLINT
+	void __iomem *clint;	/* clint base address */
+#endif
 };
 
 #include <asm-generic/global_data.h>
diff --git a/arch/riscv/include/asm/syscon.h b/arch/riscv/include/asm/syscon.h
new file mode 100644
index 0000000..d311ee6
--- /dev/null
+++ b/arch/riscv/include/asm/syscon.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#ifndef _ASM_SYSCON_H
+#define _ASM_SYSCON_H
+
+/*
+ * System controllers in a RISC-V system
+ *
+ * So far only SiFive's Core Local Interruptor (CLINT) is defined.
+ */
+enum {
+	RISCV_NONE,
+	RISCV_SYSCON_CLINT,	/* Core Local Interruptor (CLINT) */
+};
+
+#endif /* _ASM_SYSCON_H */