riscv: nx25: include: Add header files to support RISC-V

Add header files for RISC-V.
Cache, ptregs, data type and other definitions are included.

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Signed-off-by: Greentime Hu <green.hu@gmail.com>
diff --git a/arch/riscv/include/asm/linkage.h b/arch/riscv/include/asm/linkage.h
new file mode 100644
index 0000000..60d5317
--- /dev/null
+++ b/arch/riscv/include/asm/linkage.h
@@ -0,0 +1,12 @@
+/*
+ * U-Boot - linkage.h
+ *
+ * Copyright (c) 2005-2007 Analog Devices Inc.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __ASM_LINKAGE_H
+#define __ASM_LINKAGE_H
+
+#endif