gallium: Add back pipe_rasterizer_state::offset_units_unscaled

The field was removed with the nine removal but it is needed for depth
bias control on Vulkan.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26282>

src/gallium/include/pipe/p_state.h

@@ -180,6 +180,12 @@ struct pipe_rasterizer_state
     */
    unsigned clip_halfz:1;
 
+   /**
+    * When true do not scale offset_units and use same rules for unorm and
+    * float depth buffers.
+    */
+   unsigned offset_units_unscaled:1;
+
    /**
     * Depth values output from fragment shader may be outside 0..1.
     * These have to be clamped for use with UNORM buffers.