common: Move random-number functions into their own header

Create a new rand.h header file and move functions into it, to reduce
the size of common.h

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/rand.h

@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * (C) Copyright 2000-2009
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ */
+
+#ifndef __RAND_H
+#define __RAND_H
+
+#define RAND_MAX -1U
+
+/**
+ * srand() - Set the random-number seed value
+ *
+ * This can be used to restart the pseudo-random-number sequence from a known
+ * point. This affects future calls to rand() to start from that point
+ *
+ * @seed: New seed
+ */
+void srand(unsigned int seed);
+
+/**
+ * rand() - Get a 32-bit pseudo-random number
+ *
+ * @returns next random number in the sequence
+ */
+unsigned int rand(void);
+
+/**
+ * rand_r() - Get a 32-bit pseudo-random number
+ *
+ * This version of the function allows multiple sequences to be used at the
+ * same time, since it requires the caller to store the seed value.
+ *
+ * @seed value to use, updated on exit
+ * @returns next random number in the sequence
+ */
+unsigned int rand_r(unsigned int *seedp);
+
+#endif