radeon_winsys.h: add a winsys parameter to most winsys buffer functions

This will allow removing the winsys pointer from buffers.

The amdgpu winsys adds dummy_ws to get radeon_winsys because there can be
no radeon_winsys around (e.g. while amdgpu_winsys is being destroyed), but
we still need some way to call buffer functions.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9809>

src/gallium/drivers/r600/r600_asm.c

@@ -2778,7 +2778,7 @@ void *r600_create_vertex_fetch_shader(struct pipe_context *ctx,
 	} else {
 		memcpy(bytecode, bc.bytecode, fs_size);
 	}
-	rctx->b.ws->buffer_unmap(shader->buffer->buf);
+	rctx->b.ws->buffer_unmap(rctx->b.ws, shader->buffer->buf);
 
 	r600_bytecode_clear(&bc);
 	return shader;