Add VAAPI VPP support for deinterlacing

This still needs some testing, but it already works quite nice.
The new VPP API is currently only available in the staging branch of libva, but the code contains checks so it doesn't fail to compile with older vaapi versions.

I'm still very new to XBMC code, so i'm not sure if i did everything the right way.

Some people i was told who might be interested in this:
@elupus
@fernetmenta
@gbeauchesne