drm/i915: Get rid of intel_crtc->config in crtc_enable/disable functions, v2.

These functions already have a pointer to the correct state,
so use it instead of crtc->config.

Changes since v1:
- Move pll changes to the pll patch.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181004094604.2646-14-maarten.lankhorst@linux.intel.com