nir: add amul flag

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31964>

src/compiler/nir/nir.h

@@ -4167,6 +4167,13 @@ typedef struct nir_shader_compiler_options {
    /** Backend supports ternary addition */
    bool has_iadd3;
 
+   /**
+    * Backend supports amul and would like them generated whenever
+    * possible. This is stronger than has_imul24 for amul, but does not imply
+    * support for imul24.
+    */
+   bool has_amul;
+
    /**
     * Backend supports imul24, and would like to use it (when possible)
     * for address/offset calculation.  If true, driver should call