drm/i915: Show machine type in error state

As the question of 32b/64b kernels became relevant in the light of
certain bugs, include that information in the error state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190103101245.15100-1-chris@chris-wilson.co.uk