zink: reject native blits for emulated alpha formats

these need u_blitter

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17687>

src/gallium/drivers/zink/zink_blit.c

@@ -1,4 +1,5 @@
 #include "zink_context.h"
+#include "zink_format.h"
 #include "zink_kopper.h"
 #include "zink_helpers.h"
 #include "zink_query.h"
@@ -137,6 +138,8 @@ blit_native(struct zink_context *ctx, const struct pipe_blit_info *info, bool *n
    if (src->format != zink_get_format(screen, info->src.format) ||
        dst->format != zink_get_format(screen, info->dst.format))
       return false;
+   if (zink_format_is_emulated_alpha(info->src.format))
+      return false;
 
    if (!(src->obj->vkfeats & VK_FORMAT_FEATURE_BLIT_SRC_BIT) ||
        !(dst->obj->vkfeats & VK_FORMAT_FEATURE_BLIT_DST_BIT))