drm/i915: Introduce a for_each_intel_crtc() macro

Fed up with having that long list_for_each_entry() invocation?

Use for_each_intel_crtc()!

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>