r600g: adapt to latest interfaces changes

r600g: adapt to latest interfaces changes

- Wrapped the buffer and texture create/destroy/transfer/... functions
  using u_resource, which is then used to implement the resource functions.
- Implemented texture transfers.
  I left the buffer and texture transfers separate because one day we'll
  need a special codepath for textures.
- Added index_bias to the draw_*elements functions.
- Removed nonexistent *REP and *FOR instructions.
- Some pipe formats have changed channel ordering, so I've removed/fixed
  nonexistent ones.
- Added stubs for create/set/destroy sampler views.
- Added a naive implementation of vertex elements state (new CSO).
- Reworked {texture,buffer}_{from,to}_handle.
- Reorganized winsys files, removed dri,egl,python directories.
- Added a new build target dri-r600.