lpc_aspeed: add mapped file descriptor

Add mapped file descriptor that will be opened once the library tries to
copy data out of the region mapped.

Note: It may end up being mmapped before the ioctl call, as of now it's
unknown as the previous implementation of this mmap'd against /dev/mem
and not the lpc-aspeed-ctrl device.

Change-Id: I2eb898bd1f59d6be780d7c9783d6f7b2205b965b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/lpc_aspeed.hpp b/lpc_aspeed.hpp
index 53fe39b..f3608d0 100644
--- a/lpc_aspeed.hpp
+++ b/lpc_aspeed.hpp
@@ -30,6 +30,7 @@
 
   private:
     static const std::string lpcControlPath;
+    int mappedFd = -1;
     std::uint32_t regionAddress;
     std::size_t regionSize;
     const internal::Sys* sys;