CrystalHD: Add AVOption to configure hardware downscaling.
The CrystalHD hardware can do scaling, which is particularly
desirable when dealing with some high resolution clips that take
so long to decode and copy out that they end up playing back
slower than realtime. By using scaling, we can make the output
frames smaller and reduce the copy out time.
This option takes the desired horizontal width in pixels, and
the hardware will do an aspect-scale. Upscaling is not supported
and the hardware will simply ignore any request to do so.
Signed-off-by: Philip Langdale <firstname.lastname@example.org>