drm/i915/gt: Pin the rings before marking active

On eviction, we acquire the vm->mutex and then wait on the vma->active.
Therefore when binding and pinning the vma, we must follow the same
sequence, lock/pin the vma then mark it active. Otherwise, we mark the
vma as active, then wait for the vm->mutex, and meanwhile the evictor
holding the mutex waits upon us to complete our activity.

Fixes: 8ccfc20a ("drm/i915/gt: Mark ring->vma as active while pinned")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.6+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200706170138.8993-1-chris@chris-wilson.co.uk