lib: strto: add simple_strtoll function

Add simple_strtoll function for converting a string containing digits
into a long long int value.
Signed-off-by: NRoland Gaudig <roland.gaudig@weidmueller.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

include/vsprintf.h

@@ -41,6 +41,7 @@ int strict_strtoul(const char *cp, unsigned int base, unsigned long *res);
 unsigned long long simple_strtoull(const char *cp, char **endp,
 					unsigned int base);
 long simple_strtol(const char *cp, char **endp, unsigned int base);
+long long simple_strtoll(const char *cp, char **endp, unsigned int base);
 
 /**
  * trailing_strtol() - extract a trailing integer from a string

lib/strto.c

@@ -143,6 +143,14 @@ unsigned long long simple_strtoull(const char *cp, char **endp,
 	return result;
 }
 
+long long simple_strtoll(const char *cp, char **endp, unsigned int base)
+{
+	if (*cp == '-')
+		return -simple_strtoull(cp + 1, endp, base);
+
+	return simple_strtoull(cp, endp, base);
+}
+
 long trailing_strtoln(const char *str, const char *end)
 {
 	const char *p;