iris: store workaround address

This will allow to select a different address later, leaving the
beginning of the buffer to some other use.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3203>

src/gallium/drivers/iris/iris_screen.h

@@ -136,6 +136,12 @@ struct iris_vtable {
    void (*lost_genx_state)(struct iris_context *ice, struct iris_batch *batch);
 };
 
+struct iris_address {
+   struct iris_bo *bo;
+   uint64_t offset;
+   bool write;
+};
+
 struct iris_screen {
    struct pipe_screen base;
 
@@ -190,6 +196,7 @@ struct iris_screen {
     * require scratch writes or reads from some unimportant memory.
     */
    struct iris_bo *workaround_bo;
+   struct iris_address workaround_address;
 
    struct disk_cache *disk_cache;
 };