add dppOracle

contracts/DODOPrivatePool/intf/IOracle.sol

@@ -0,0 +1,12 @@
+/*
+
+    Copyright 2021 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+
+interface IOracle {
+    function getPrice(address base) external view returns (uint256 latestPrice,bool isValid,bool isStale,uint256 timestamp);    
+}