lib: Add function to extract a number from the end of a string

Split out the code in fdtdec which finds a number at the end of a string. It
can be useful in other situations.

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/vsprintf.c

@@ -166,6 +166,25 @@ unsigned long long simple_strtoull(const char *cp, char **endp,
 	return result;
 }
 
+long trailing_strtoln(const char *str, const char *end)
+{
+	const char *p;
+
+	if (!end)
+		end = str + strlen(str);
+	for (p = end - 1; p > str; p--) {
+		if (!isdigit(*p))
+			return simple_strtoul(p + 1, NULL, 10);
+	}
+
+	return -1;
+}
+
+long trailing_strtol(const char *str)
+{
+	return trailing_strtoln(str, NULL);
+}
+
 /* we use this so that we can do without the ctype library */
 #define is_digit(c)	((c) >= '0' && (c) <= '9')