gallium: Add pipe_image_view::single_layer_view

OpenGL has a goofy feature that allows creating an image view of a single layer
of an array texture... in which case that image is treated as non-arrayed in
shader. If you have a 16x16x16 3D texture and bind the third layer, you get a
16x16 2D texture instead of a 16x16x1 3D texture. That distinction matters to
the hardware on AGX, since the texture dimension needs to match between the
shader and the pipe_image_view. If the shader is going to use image2D, we need
to know that the pipe_image_view should be treated as 2D (even though the
underlying resource is 3D).

"But, Alyssa, we already have first_layer and last_layer. Surely you can just
check if first_layer == last_layer?" you ask. The problem is that doesn't
distinguish a 16x16x1 3D texture (accessed as image3D in the shader) from a
16x16 slice (accessed as image2D in the shader) of a 16x16x16 3D texture. To
solve, we add a boolean flag indicating we want to create a view (with a lower
dimension than the underlying resource). This provides an unambiguous way to
communicate this case to drivers.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23142>

src/gallium/auxiliary/util/u_dump_state.c

@@ -742,6 +742,7 @@ util_dump_image_view(FILE *stream, const struct pipe_image_view *state)
       util_dump_member(stream, uint, state, u.buf.size);
    }
    else {
+      util_dump_member(stream, bool, state, u.tex.single_layer_view);
       util_dump_member(stream, uint, state, u.tex.first_layer);
       util_dump_member(stream, uint, state, u.tex.last_layer);
       util_dump_member(stream, uint, state, u.tex.level);

src/gallium/include/pipe/p_state.h

@@ -546,6 +546,7 @@ struct pipe_image_view
          unsigned first_layer:16;     /**< first layer to use for array textures */
          unsigned last_layer:16;      /**< last layer to use for array textures */
          unsigned level:8;            /**< mipmap level to use */
+         bool single_layer_view;      /**< single layer view of array */
       } tex;
       struct {
          unsigned offset;   /**< offset in bytes */