drm/i915: Use enabled value from crtc_state rather than crtc (v2)

As vendors transition their drivers from legacy to atomic there's some
duplication of data between drm_crtc and drm_crtc_state (since
unconverted drivers likely won't have a state structure).

i915 is partially converted and does have a crtc->state structure, but
still uses direct crtc fields internally in many places, which causes
the two sets of data to get out of sync.  As of commit

        commit 31c946e8
        Author: Daniel Vetter <daniel.vetter@ffwll.ch>
        Date:   Sun Feb 22 12:24:17 2015 +0100

            drm: If available use atomic state in getcrtc ioctl

            This way drivers fully converted to atomic don't need to update these
            legacy state variables in their modeset code any more.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

the DRM core starts assuming that the presence of a ->state structure
implies that it should make use of the values stored there which, on
i915, leads to the core code using stale values for CRTC 'enabled'
status.

Let's switch over to using the state value of 'enable' internally rather
than using the drm_crtc field.  This ensures that our driver internals
are working from the same data that the DRM core is, avoiding
mismatches.

This patch was generated with Coccinelle using the following semantic
patch:

        <smpl>
        @@
        struct drm_crtc C;
        struct drm_crtc *CP;
        @@
        (
        - C.enabled
        + C.state->enable
        |
        - CP->enabled
        + CP->state->enable
        )

        // For assignments, we still update the legacy value as well as the state value
        // so add an extra assignment statement for that.
        @@
        struct drm_crtc C;
        struct drm_crtc *CP;
        expression E;
        @@
        (
          C.state->enable = E;
        + C.enabled = E;
        |
          CP->state->enable = E;
        + CP->enabled = E;
        )
        </smpl>

The crtc->mode and crtc->hwmode fields should probably be transitioned
over as well eventually, but we seem to do an okay job of keeping those
up-to-date already so I want to minimize the changes that will clash
with Ander's in-progress atomic work.

v2: Don't remove the assignments to the legacy value when we assign to
    the state value.  A second cocci stanza takes care of adding the
    legacy assignment back where appropriate.  (Daniel)

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>