graw: Undo late loading of graw drivers.

graw: Undo late loading of graw drivers.

Keith prefers a clean separation between graw applications and
implementations, where apps do not link libgallium.a but instead
get all functionality they need via graw interface.

Although this is not incompatible with late loading of graw drivers, it
it would make it very hard to maintain, as wrappers for every utility
symbol exposed in graw would have to be written or generated somehow.