gallium: add pipe_blit_info::dst_sample, update u_blitter to write that sample

A new radeonsi blit test will use it to upload different sample values
into MSAA textures.

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17694>

src/gallium/drivers/zink/zink_render_pass.c

@@ -701,7 +701,7 @@ zink_begin_render_pass(struct zink_context *ctx)
          util_blitter_blit_generic(ctx->blitter, dst_view, &dstbox,
                                    src_view, &dstbox, ctx->fb_state.width, ctx->fb_state.height,
                                    PIPE_MASK_RGBAZS, PIPE_TEX_FILTER_NEAREST, NULL,
-                                   false, false);
+                                   false, false, 0);
 
          pipe_sampler_view_reference(&src_view, NULL);
          csurf->transient_init = true;