drm/i915: reinstate call to trace_i915_vma_bind

drm/i915: reinstate call to trace_i915_vma_bind

The call went away in:

commit 3b16525cc4c1a43e9053cfdc414356eea24bdfad
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu Aug 4 16:32:25 2016 +0100

    drm/i915: Split insertion/binding of an object into the VM

It is useful to have this trace as it pairs nicely with the vma_unbind
one to track vma activity.
Added inside the i915_vma_bind function (was outside before) to keep a
similar placement as trace_i915_vma_unbind.

v2: print bind_flags instead of flags (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1484949083-11430-1-git-send-email-daniele.ceraolospurio@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>