drm/i915: Don't forget to mark crtc as inactive after disable

Watermark calculations depend on the intel_crtc->active flag to be set
properly. Suspend/resume is broken on SKL and we also get DDB mismatches
without this patch.

The regression was introduced in:

commit eddfcbcd


Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date:   Mon Jun 15 12:33:53 2015 +0200

    drm/i915: Update less state during modeset.

    No need to repeatedly call update_watermarks, or update_fbc.
    Down to a single call to update_watermarks in .crtc_enable

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
    Tested-by(IVB): Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

v2: Don't touch disable_shared_dpll()

Signed-off-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91203
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>