Misc. cleanups

Just some cleanups for unused fields in drm_crtc.h and some comment corrections. I also removed a few DRM_ERRORs from drm_crtc.c (things actually weren't as bad as I feared).

Next step is to remove a whole slew of DRM_DEBUG calls unless people are really attached to them. I find them to just get in the way when I'm debugging a display problem, so I convert the ones I care about to DRM_ERROR temporarily and add several of my own...

Thanks, Jesse