drm/i915: Quirk the pipe A quirk in the modeset state checker

drm/i915: Quirk the pipe A quirk in the modeset state checker

If we always force the pipe A to on we can't use the hw state to
decide whether it should be on. Hence quirk the quirk.

The problem is that crtc->active tracks the state of the entire
display pipe, i.e. including planes, encoders and all. But our hw
state readout simply looks at the pipe. But with the pipe A quirk we
force-enable that (together with it's pll). To fix that mismatch we
have two options:
- Quirk the checked state to match what our sw tracking states if the
  pipe A quirk is in effect.
- Improve the hw state readout to not get fooled by the pipe A quirk.

Since we already have similar state clamping in e.g. assert_pipe I've
opted for the first variant. Also note that we don't really loose any
state checking: Individual pieces of the abstract crtc pipe are
checked in the enable/disable functions with the various asssert_*
checks we have, and the hw state check code doesn't check anything if
the pipe is off anyway.

v2: Pimp commit message after discussion with Chris and only apply the
quirk for the quirk if we're checking pipe A. Otherwise we'll miss
state checking for pipe B on i830M ...

v3: Make the code comment consistent with the improved commit message,
too (Chris).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=64764
Cc: stable@vger.kernel.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reported-and-Tested-by: mlsemon35@gmail.com (v1)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>