drm/i915: Ignore applying the self-relocation BIAS if no relocations

drm/i915: Ignore applying the self-relocation BIAS if no relocations

We only need to apply the BIAS for self-relocations into the batchbuffer
iff the execobject has any relocations.

This suppresses some warnings we may get with a full gtt (so the batch
object has wound up at 0 from a previous invocation), but doesn't fix
the underlying problem of how we tried to move a pinned batch vma (how
we have a pinned user vma outside of execbuf, I do not know, though this
being on an aliasing ppgtt means it could be a spurious pinning via the
global gtt). One step at a time...

References: https://bugs.freedesktop.org/show_bug.cgi?id=106744#c1
Testcase: igt/gem_exec_gttfill # byt (sporadic)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180621073205.26701-1-chris@chris-wilson.co.uk