r600g: implement transform feedback

r600: DONE.
r700: MOSTLY (done but locks up).
Evergreen: MOSTLY (done but doesn't work for an unknown reason).

The kernel support will come soon.
diff --git a/src/gallium/drivers/r600/r600_hw_context_priv.h b/src/gallium/drivers/r600/r600_hw_context_priv.h
index bea6135..206de7e 100644
--- a/src/gallium/drivers/r600/r600_hw_context_priv.h
+++ b/src/gallium/drivers/r600/r600_hw_context_priv.h
@@ -76,6 +76,13 @@
 void r600_init_cs(struct r600_context *ctx);
 int r600_resource_init(struct r600_context *ctx, struct r600_range *range, unsigned offset, unsigned nblocks, unsigned stride, struct r600_reg *reg, int nreg, unsigned offset_base);
 
+/*
+ * evergreen_hw_context.c
+ */
+void evergreen_flush_vgt_streamout(struct r600_context *ctx);
+void evergreen_set_streamout_enable(struct r600_context *ctx, unsigned buffer_enable_bit);
+
+
 static INLINE unsigned r600_context_bo_reloc(struct r600_context *ctx, struct r600_resource *rbo,
 					     enum radeon_bo_usage usage)
 {