CONFIG_PSERIES_PLPKS is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PSERIES_PLPKS (not configurable)

modulename: plpks.ko

configname: CONFIG_PSERIES_PLPKS

Linux Kernel Configuration
└─>PSERIES_PLPKS
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
source code:
arch/powerpc/platforms/pseries/plpks.c
selects
CONFIG_NLS