drm/i915: Remove all ->config dereferences from intel_hdmi, v2.

drm/i915: Remove all ->config dereferences from intel_hdmi, v2.

In all cases we can now obtain the relevant crtc_state/conn_state
from the relevant callbacks, which means all the ->config accesses
can be removed and the code cleaned up.

Changes since v1:
- cstate -> crtc_state

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/8b02a6b4-606a-e43a-b357-ad17f491525b@linux.intel.com
[mlankhorst: Reinstate missing comment]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>