Comment # 2 on bug 1118048 from Stefan Dirsch

libvdpau_r600/libvdpau_r300/libvdpau_radeonsi are selected if xf86-video-ati
gets selected. xf86-video-ati gets selected if you own an ATI/AMD card, i.e. a
GPU with Vendor ID 1002. xf86-video-mach64/r128 also gets autoselected by this
Vendor ID. You can safely unselect/uninstall these packages. It would be
tremendous work to figure all Device IDs, which are supported by these drivers
and maintain these lists. The drivers aren't used if they don't support the
hardware. So I would say  better safe than sorry.