window interface: add close method

Add a close method, that when called does whatever is appropriate for
the given implementation.

Note: There are a few methods that don't map nicely, and therefore it
makes sense to add a close() to this interface.

Change-Id: If001446b2248715ea76147ea35a99a729ba5a404
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/lpc_aspeed.cpp b/lpc_aspeed.cpp
index dabea8a..50ce2a9 100644
--- a/lpc_aspeed.cpp
+++ b/lpc_aspeed.cpp
@@ -43,6 +43,10 @@
     return std::make_unique<LpcMapperAspeed>(regionAddress, regionSize);
 }
 
+void LpcMapperAspeed::close()
+{
+}
+
 std::pair<std::uint32_t, std::uint32_t>
     LpcMapperAspeed::mapWindow(std::uint32_t address, std::uint32_t length)
 {