lib: Add a way to find the postiion of a trailing number

At present it is not possible to find out which part of the string is the
number part and which is before it. Add a new variant which provides this
feature, so we can separate the two in the caller.

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

include/vsprintf.h

@@ -121,6 +121,24 @@ long trailing_strtol(const char *str);
  */
 long trailing_strtoln(const char *str, const char *end);
 
+/**
+ * trailing_strtoln_end() - extract trailing integer from a fixed-length string
+ *
+ * Given a fixed-length string this finds a trailing number on the string
+ * and returns it. For example, "abc123" would return 123. Only the
+ * characters between @str and @end - 1 are examined. If @end is NULL, it is
+ * set to str + strlen(str).
+ *
+ * @str:	String to examine
+ * @end:	Pointer to end of string to examine, or NULL to use the
+ *		whole string
+ * @endp:	If non-NULL, this is set to point to the character where the
+ *	number starts, e.g. for "mmc0" this would be point to the '0'; if no
+ *	trailing number is found, it is set to the end of the string
+ * Return: training number if found, else -1
+ */
+long trailing_strtoln_end(const char *str, const char *end, char const **endp);
+
 /**
  * panic() - Print a message and reset/hang
  *