drm/i915/selftests: ditch the kernel context

There's really no good reason to be using the kernel context for the
huge-page livetests. Also with the introduction of commit bef27bdb
("drm/i915: Assert we do not try to expand VMA for hugepage inside GGTT")
we start hitting the bug on in the selftests, since the kernel context
will always return true for i915_vma_is_ggtt(), so now seems like the
opportune time to instead create our own context.

Fixes: 4049866f ("drm/i915/selftests: huge page tests")
Fixes: bef27bdb ("drm/i915: Assert we do not try to expand VMA for hugepage inside GGTT")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171010133030.12112-1-matthew.auld@intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>