Kbuild: Make composite object searching more generic

Reduce repeated logic around expanding composite objects in preparation
for later commit to support nested composite objects.

Change-Id: I9f2f4788bd4a85f105432e4827f9984cd488b647
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Signed-off-by: Jeff Johnson <jjohnson@codeaurora.org>