i965g: clean up winsys interface

  enum intel_ring_type         -> enum intel_exec_flag
  winsys->enable_fenced_relocs -> gone
  winsys->alloc                -> winsys->alloc_buffer (with change)
  winsys->alloc_tiled          -> winsys->alloc (with change)
  winsys->alloc_from_handle    -> winsys->import_handle (with change)
  winsys->decode_batch         -> winsys->decode_commands
  bo->get_gem_handle           -> gone
  bo->get_handle               -> bo->export_handle
  bo->wait_rendering           -> bo->wait (with change)
  bo->busy                     -> intel_bo_is_busy
  bo->subdata                  -> bo->pwrite
  bo->get_subdata              -> bo->pread