video: add vdpau acceleration support

Adds the VDPAU acceleration for GNU/Linux systems and
enable it by devault. Can be disabled using ./configure --disable-vdpau

Support for H.264, H.263 and MPEG4, as long as the hardware supports
them.

Requires libvdpau and ffmpeg 3.3 (contrib bump included by this patch)

[guillaume roguez: re-word ci msg to be more explicit]

Change-Id: I7479f4d7e3d51caf702be8c85284a4fca01605b3
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>
7 files changed