firmware: add read/write configuration methods

A data handler may require the host-side client to read or write
configuration information.  Therefore, implement a method for
controlling this in the data handler object.

Change-Id: Id7f8ff54d90cece2e8751773a8696638c2a2ea77
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/data_mock.hpp b/test/data_mock.hpp
index 1fd1fae..a79c562 100644
--- a/test/data_mock.hpp
+++ b/test/data_mock.hpp
@@ -13,6 +13,8 @@
     virtual ~DataHandlerMock() = default;
 
     MOCK_METHOD1(copyFrom, std::vector<std::uint8_t>(std::uint32_t));
+    MOCK_METHOD1(write, bool(const std::vector<std::uint8_t>&));
+    MOCK_METHOD0(read, std::vector<std::uint8_t>());
 };
 
 } // namespace blobs