Add device-tests and general-tests make targets.

Adds the device-tests and general-tests makefiles and
added include lines to main.mk so that individual test
modules can be built properly.

These targets do not build any special tradefed wrapper
that normal *TS's usually employ. They are not necessary
here.

Bug: 35350788
Test: Updated several CTS test modules to belong to these
      suites instead and ran:
      `rm -rf out; make clean; make device-tests general-tests -j`
      then verified the output.

Change-Id: I40e3958375f7b39cb56508f2812ce9760d403f6f
diff --git a/core/main.mk b/core/main.mk
index dff0163..c131ed2 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -90,6 +90,10 @@
 -include cts/build/config.mk
 # VTS-specific config.
 -include test/vts/tools/vts-tradefed/build/config.mk
+# device-tests-specific-config.
+-include tools/tradefederation/build/suites/device-tests/config.mk
+# general-tests-specific-config.
+-include tools/tradefederation/build/suites/general-tests/config.mk
 
 # This allows us to force a clean build - included after the config.mk
 # environment setup is done, but before we generate any dependencies.  This