iris: Retry DRM_IOCTL_I915_GEM_EXECBUFFER2 on ENOMEM

We are seeing endless DRM_IOCTL_SYNCOBJ_WAIT ioctl when system memory is under pressured.

Commit f9d8d9ac ("iris: Avoid abort() if kernel can't allocate memory") avoids the abort() on ENOMEM by resetting the batch. However, when there's an ongoing OpenGL query, resetting the batch will make the snapshots_landed never be flipped, so iris_get_query_result() gets stuck in the while loop forever.

Since there's no guarantee that the next batch after resetting won't hit ENOMEM, so instead of resetting the batch, be patient and wait until kernel has enough memory. Once the batch is submiited and snapshots_landed gets flipped, iris_get_query_result() can proceed normally.

Closes: drm/intel#6851