hash handler: implement file hash handler

Implement the hash handler as a generic file handler as there is not
likely to be any magic required for it.

Change-Id: I82ac102c720718504aa3dbcae0b13031349d6121
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 7455b4d..bd7e932 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,7 @@
 	static_handler.cpp \
 	lpc_handler.cpp \
 	pci_handler.cpp \
-	hash_handler.cpp
+	file_handler.cpp
 libfirmwareblob_la_LDFLAGS = \
 	$(PHOSPHOR_LOGGING_LIBS) \
 	-version-info 0:0:0 -shared