tools: add io interface for mmio, etc

Add an IO interface for host-side memory access.  This is done as an
interface to allow platform specific implementations.

Change-Id: Id8e35d5beb21f7db544e27d6592bbeac58748dcb
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/tools/Makefile.am b/tools/Makefile.am
index 61d2907..05daf75 100644
--- a/tools/Makefile.am
+++ b/tools/Makefile.am
@@ -14,4 +14,5 @@
 	blob_handler.cpp \
 	ipmi_handler.cpp \
 	crc.cpp \
+	io.cpp \
 	../internal/sys.cpp