arm64: Configure iMX OCOTP driver as built-in

Task: https://phabricator.apertis.org/T8567

The iMX8MN SoC comes with an OCOTP module, where the FEC MAC address is stored. The iMX OCOTP driver is built as a module but it's not included in the initrd, so the ethernet device is not getting registered.

In order to support NFS rootfs, the initrd needs to setup the ethernet device, so let's enable the required OCOTP driver as built-in.