Make: Move testing into a subdirectory

In preparation for expanding the testing, move the test targets
out of the top level Makefile.inc and into a separate
subdirectory.

Change-Id: Ie252c7555223f9ce76b54e6f7b66d03f3cf60500
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20873
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Chris Ching <chingcodes@google.com>
3 files changed