drm/i915/selftests: Use NOWARN for large allocations

drm/i915/selftests: Use NOWARN for large allocations

We may try to do a large kmalloc for the permutation array, falling back
to a smaller array/test if the first allocation fails. Since we are
intentionally trying a large allocation which may fail, pass __GFP_NOWARN.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103842
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171122120600.27025-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>