[Intel-gfx] [RFC i-g-t 1/6] tests/gem_pread: drop stolen memory related subtests

[Chris Wilson]

Quoting Daniele Ceraolo Spurio (2017-10-03 00:00:13)
> The feature was never merged and there has been no progress in the
> last year. The subtests are currently skipping on all platforms by
> checking a field in the get_aperture ioctl structure that doesn't
> exist in the kernel version of the struct.

The interface for this is upstream, fix the test to exercise the kernel
code (hint dmabuf).
-Chris