Commit0543eb1110("imx6: 5.4: add missing kernel perf monitor symbol") has added missing kernel config symbol FSL_IMX8_DDR_PMU which is exposed only when building perf, so add it back. Fixes:8d9b36270b("imx6: refresh kernel config") Signed-off-by: Petr Štetiar <ynezz@true.cz>