firmware: add sdbusplus for use by verification

The verification process starts a systemd service implemented outside
the scope of this codebase.  Therefore, add sdbusplus to the build and
inject into the object.

Change-Id: Icaacb5d60334da78f6363682f3b97714eb482dcf
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 3d0d93c..100ba92 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -11,9 +11,11 @@
 	lpc_aspeed.cpp \
 	lpc_nuvoton.cpp
 libfirmwareblob_la_LDFLAGS = \
+	$(SDBUSPLUS_LIBS) \
 	$(PHOSPHOR_LOGGING_LIBS) \
 	-version-info 0:0:0 -shared
 libfirmwareblob_la_CXXFLAGS = \
+	$(SDBUSPLUS_CFLAGS) \
 	$(PHOSPHOR_LOGGING_CFLAGS) \
 	-flto