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/test/Makefile.am b/test/Makefile.am
index 2af6033..731a030 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -2,11 +2,13 @@
 	$(GTEST_CFLAGS) \
 	$(GMOCK_CFLAGS)
 AM_CXXFLAGS = \
-	$(GTEST_MAIN_CFLAGS)
+	$(GTEST_MAIN_CFLAGS) \
+	$(SDBUSPLUS_CFLAGS)
 AM_LDFLAGS = \
 	$(GMOCK_LIBS) \
 	$(GTEST_MAIN_LIBS) \
-	$(OESDK_TESTCASE_FLAGS)
+	$(OESDK_TESTCASE_FLAGS) \
+	$(SDBUSPLUS_LIBS)
 
 # Run all 'check' test programs
 check_PROGRAMS = \