vsprintf: add ustrtoll function

Add 'ustrtoull' function to convert size from string (ex: 1GiB)
to unsigned long long type

Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
diff --git a/include/exports.h b/include/exports.h
index 6cf31aa..41d5085 100644
--- a/include/exports.h
+++ b/include/exports.h
@@ -24,6 +24,7 @@
 long simple_strtol(const char *cp,char **endp,unsigned int base);
 int strcmp(const char * cs,const char * ct);
 unsigned long ustrtoul(const char *cp, char **endp, unsigned int base);
+unsigned long long ustrtoull(const char *cp, char **endp, unsigned int base);
 #if defined(CONFIG_CMD_I2C)
 int i2c_write (uchar, uint, int , uchar* , int);
 int i2c_read (uchar, uint, int , uchar* , int);