cdv: continue synching up with updated reference code

In particular clean up the errata handling and correct the crtc masks. We do
this a bit differently using our device abstraction for neatness.

This doesn't address the ACPI opregion and hotplug plumbing, nor the IRQ related
changes that will need. It touches on backlight init but the full backlight
support is not in this change set.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>