intel: Disable loading drivers on DG1 devices for now

Kernel support for DG1 has not yet been merged upstream; per our long-standing DRM subsystem policy, we should not enable the platform in userspace until the kernel patches are merged and functional.

We will re-enable this in the future. In the meantime, we retain all of the infrastructure and code for the platform so that we can continue developing DG1 support in upstream.

See a discussion here: !4956 (comment 547775)