drm/i915: Disallow pin ioctl completely for kms drivers

drm/i915: Disallow pin ioctl completely for kms drivers

The problem here is that SNA pins batchbuffers to etch out a bit more
performance. Iirc it started out as a w/a for i830M (which we've
implemented in the kernel since a long time already). The problem is
that the pin ioctl wasn't added in

commit 8b1eadd7b00b31aff90f4bfd17c1d1b3b0042566
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Fri May 23 08:48:08 2014 +0200

    drm/i915: Prevent negative relocation deltas from wrapping

Fix this by simply disallowing pinning from userspace so that the
kernel is in full control of batch placement again. Especially since
distros are moving towards running X as non-root, so most users won't
even be able to see any benefits.

UMS support is dead now, but we need this minimal patch for
backporting. Follow-up patch will remove the pin ioctl code
completely.

Note to backporters: You must have both

commit 82634f88cb2e311286f4eef81ec1c4b9c0c33d35
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Dec 17 16:21:27 2012 +0100

    drm/i915: Implement workaround for broken CS tlb on i830/845

which laned in 3.8 and

commit d38460cfd2cde8ebc6c03c6b4732284a3a7f1257
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Sep 8 14:25:41 2014 +0100

    drm/i915: Evict CS TLBs between batches

which is also marked cc: stable. Otherwise this could introduce a
regression by disabling the userspace w/a without the kernel w/a being
fully functional on i830/45.

References: https://bugs.freedesktop.org/show_bug.cgi?id=76554#c116
Cc: stable@vger.kernel.org # requires d38460cfd2cde8ebc6c and v3.8
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>