OPT driver of fsl-imx6 is not enabled.
Apply attached patch. And enable CONFIG_FSL_OTP kernel option.
1. Configure a project: .../wrlinux/configure --enable-board=fsl-imx6 --enable-kernel=standard --enable-rootfs=glibc_small --enable-parallel-pkgbuilds=8 2. Build 3. Boot on target, check if /sys/fsl_otp/ exists or not.