nir: gather which images are buffers

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5209>

src/compiler/shader_info.h

@@ -152,6 +152,8 @@ typedef struct shader_info {
 
    /** Bitfield of which images are used */
    uint32_t images_used;
+   /** Bitfield of which images are buffers. */
+   uint32_t image_buffers;
 
    /* SPV_KHR_float_controls: execution mode for floating point ops */
    uint16_t float_controls_execution_mode;