Create a single library (for the vdpau api) thus reducing
the overall size of mesa. Current commit converts
vdpau-nouveau, with upcomming commits handling the rest.

The library can be built with the relevant pipe-drivers
statically linked in, or loaded as shared modules.
Currently we default to static.

Add SPLIT_TARGETS to guard the other VL targets.

Note: symlink handling is rather ugly and will need an
update to work with BSD and other non-linux platforms.

v2: Split the conversion into per-target basis.

Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Tested-by: Thomas Helland <thomashelland90 at gmail.com>