nir/lower_tex: Add support for lowering coordinate offsets

On i965, we can't support coordinate offsets for texelFetch or rectangle
textures.  Previously, we were doing this with a GLSL pass but we need to
do it in NIR if we want those workarounds for SPIR-V.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "12.0" <mesa-dev@lists.freedesktop.org>

src/compiler/nir/nir.h

@@ -2408,6 +2408,16 @@ typedef struct nir_lower_tex_options {
     */
    unsigned lower_txp;
 
+   /**
+    * If true, lower away nir_tex_src_offset for all texelfetch instructions.
+    */
+   bool lower_txf_offset;
+
+   /**
+    * If true, lower away nir_tex_src_offset for all rect textures.
+    */
+   bool lower_rect_offset;
+
    /**
     * If true, lower rect textures to 2D, using txs to fetch the
     * texture dimensions and dividing the texture coords by the