[PATCH 0/2][Lucid SRU] Fix i915 BUG due to unreferenced object

[Seth Forshee]

BugLink: http://bugs.launchpad.net/bugs/843904

SRU Justification

Impact: The i915 driver is not holding references to DRM objects during
eviction. Thus an object could be freed while i915 is still referencing
it, which results in a kernel BUG and an xserver freeze.

Fix: Backport of upstream fix to hold references to objects during
eviction and a related fix to object cleanup in the error paths.

Test case: Verified on LP #843904.

Note that the substantive portions of the second patch were already
applied in an earlier backport. The remaining changes are fairly trivial
and aren't strictly necessary for this bug, but I've included them here
to bring the code more in line with upstream.