drm/atomic: Fix atomic helpers to use the new iterator macros, v3.

There are new iterator macros that annotate whether the new or old
state should be used. This is better than using a state that depends on
whether it's called before or after swap. For clarity, also rename the
variables from $obj_state to (old,new)_$obj_state as well.

Changes since v1:
- Use old/new_*_state for variable names as much as possible. (pinchartl)
- Expand commit message.
Changes since v2:
- Rebase on top of link training patches.
- free -> cleanup (pinchartl)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: http://patchwork.freedesktop.org/patch/msgid/aafa0d4d-474d-441f-3685-fa6c042ef37e@linux.intel.comTested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>