display: hal: Conditionally build HAL modules

* QTI composer service and sdmcore have proprietary header dependency
on Pixelworks projects.
* Hence, allow the modules to be hidden when proprietary headers
are not present in source tree.

Issue: FP4-INT#3
Change-Id: I0c3c7bc57f63eb576a27c4a735767b49c0924be9
2 files changed