drm: Clean up drm_crtc.h

- Group declarations for separate files (drm_bridge.c, drm_edid.c)
- Move declarations only used within drm.ko to drm_crtc_internal.h
- drm_property_type_valid to drm_crtc.c, its only callsite

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466499262-18717-2-git-send-email-daniel.vetter@ffwll.ch