nir: Add and set info::uses_64bit

Will be used to communicate that a shader uses 64-bit operations to the
concerned lowering passes.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/shader_info.h

@@ -121,6 +121,11 @@ typedef struct shader_info {
     */
    bool uses_fddx_fddy;
 
+   /**
+    * True if this shader uses 64-bit ALU operations
+    */
+   bool uses_64bit;
+
    /* The size of the gl_ClipDistance[] array, if declared. */
    unsigned clip_distance_array_size;