drm/i915: Add pipe B force quirk for 830M

830M has problems when some of the pipes are disabled. Namely if a
plane, DVO port etc. is currently assigned to a disabled pipe, it
can't moved to the other pipe until the current pipe is also enabled.
To keep things simple just leave both pipes running all the time.

Ideally I think should turn the pipes off if neither is active, and
when either becomes active we enable both. But that would reuquire
proper atomic modeset support, and probably a bit of extra care in
the order things get enabled.

v2: Reorder wrt. double wide handling changes

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Thomas Richter <richter@rus.uni-stuttgart.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 13db418..dbf9a26 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -709,6 +709,7 @@
 #define QUIRK_LVDS_SSC_DISABLE (1<<1)
 #define QUIRK_INVERT_BRIGHTNESS (1<<2)
 #define QUIRK_BACKLIGHT_PRESENT (1<<3)
+#define QUIRK_PIPEB_FORCE (1<<4)
 
 struct intel_fbdev;
 struct intel_fbc_work;