x86: Move table csum into separate header

We need the checksum function without all the other table functionality
soon, so let's split it out into its own header file.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/tables_csum.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2015, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _TABLES_CSUM_H_
+#define _TABLES_CSUM_H_
+
+static inline u8 table_compute_checksum(void *v, int len)
+{
+	u8 *bytes = v;
+	u8 checksum = 0;
+	int i;
+
+	for (i = 0; i < len; i++)
+		checksum -= bytes[i];
+
+	return checksum;
+}
+
+#endif