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>

lib/strto.c

@@ -183,7 +183,7 @@ long long simple_strtoll(const char *cp, char **endp, unsigned int base)
 	return simple_strtoull(cp, endp, base);
 }
 
-long trailing_strtoln(const char *str, const char *end)
+long trailing_strtoln_end(const char *str, const char *end, char const **endp)
 {
 	const char *p;
 
@@ -192,14 +192,24 @@ long trailing_strtoln(const char *str, const char *end)
 	p = end - 1;
 	if (p > str && isdigit(*p)) {
 		do {
-			if (!isdigit(p[-1]))
+			if (!isdigit(p[-1])) {
+				if (endp)
+					*endp = p;
 				return dectoul(p, NULL);
+			}
 		} while (--p > str);
 	}
+	if (endp)
+		*endp = end;
 
 	return -1;
 }
 
+long trailing_strtoln(const char *str, const char *end)
+{
+	return trailing_strtoln_end(str, end, NULL);
+}
+
 long trailing_strtol(const char *str)
 {
 	return trailing_strtoln(str, NULL);