drm/i915: Make intel_display_suspend atomic, v2.

Calculate all state using a normal transition, but afterwards fudge
crtc->state->active back to its old value. This should still allow
state restore in setup_hw_state to work properly.

Calling intel_set_mode will cause intel_display_set_init_power to be
called, make sure init_power gets set again afterwards.

Changes since v1:
- Fix to compile with v2 of the patch that adds intel_display_suspend.
- Add intel_display_set_init_power.
- Set return value to int to allow error checking.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>