drm/i915: Don't pin LRC in GGTT when dumping in debugfs

drm/i915: Don't pin LRC in GGTT when dumping in debugfs

LRC object does not need to be mapped into the GGTT when dumping. A side-effect
of this patch is that a compiler warning goes away (not checking return value
of i915_gem_obj_ggtt_pin).

v2: Broke out individual context dumping into a new function as the indentation
was getting a bit crazy.  Added notification of contexts with no gem object for
debugging purposes.  Removed unnecessary pin_pages and unpin_pages, replaced
with explicit get_pages for the context object as there may be no backing store
allocated at this time (Comment for get_pages says "Ensure that the associated
pages are gathered from the backing storage and pinned into our object").
Improved error checking - get_pages and get_page are checked for failure.

Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
[danvet: Align paramter continuation lines properly. Also add some
braces to the nested loops again for readability.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>