drm/i915: add HAS_DDI check

And use it whenever we call code that uses the DDIs. We already have
intel_ddi.c and prefix every function with intel_ddi_something instead of
haswell_something, so I think replacing the checks with HAS_DDI makes more
sense. Just a cosmetical change, yes I know, but I have this OCD...

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 5c77743..bc07b3f 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -771,7 +771,7 @@
 
 	crt->base.disable = intel_disable_crt;
 	crt->base.enable = intel_enable_crt;
-	if (IS_HASWELL(dev))
+	if (HAS_DDI(dev))
 		crt->base.get_hw_state = intel_ddi_get_hw_state;
 	else
 		crt->base.get_hw_state = intel_crt_get_hw_state;