nir/vtn: Support SpvOpIsNormal via fisnormal

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6355>

src/compiler/spirv/vtn_alu.c

@@ -353,6 +353,8 @@ vtn_nir_alu_op_for_spirv_opcode(struct vtn_builder *b,
    case SpvOpDPdxCoarse:   return nir_op_fddx_coarse;
    case SpvOpDPdyCoarse:   return nir_op_fddy_coarse;
 
+   case SpvOpIsNormal:     return nir_op_fisnormal;
+
    default:
       vtn_fail("No NIR equivalent: %u", opcode);
    }