drm/i915: make reset&hangcheck code VM aware

Hangcheck, and some of the recent reset code for guilty batches need to
know which address space the object was in at the time of a hangcheck.
This is because we use offsets in the (PP|G)GTT to determine this
information, and those offsets can differ depending on which VM they are
bound into.

Since we still only have 1 VM ever, this code shouldn't yet have any
impact.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>