ail: Add compression_layer_stride_B field

So we can index into the compression buffer of layered images.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20446>

src/asahi/layout/layout.c

@@ -220,7 +220,8 @@ ail_initialize_compression(struct ail_layout *layout)
       height_px = DIV_ROUND_UP(height_px, 2);
    }
 
-   layout->size_B += compbuf_B * layout->depth_px;
+   layout->compression_layer_stride_B = compbuf_B;
+   layout->size_B += layout->compression_layer_stride_B * layout->depth_px;
 }
 
 void

src/asahi/layout/layout.h

@@ -125,6 +125,9 @@ struct ail_layout {
    /* Offset of the start of the compression metadata buffer */
    uint32_t metadata_offset_B;
 
+   /* Stride between subsequent layers in the compression metadata buffer */
+   uint32_t compression_layer_stride_B;
+
    /* Size of entire texture */
    uint32_t size_B;
 };