CONFIG_KERNEL_PL is not available for thedefaultarchitecture x86.
Result is shown for architecture tile

Processor protection level for kernel

configname: CONFIG_KERNEL_PL

Linux Kernel Configuration
└─>Tilera-specific configuration
└─>Processor protection level for kernel
In linux kernel since version 2.6.37 (release Date: 2011-01-04)  
Since MDE 4.2, the Tilera hypervisor runs the kernel
at PL2 by default. If running under an older hypervisor,
or as a KVM guest, you must run at PL1. (The current
hypervisor may also be recompiled with "make HV_PL=2" to
allow it to run a kernel at PL1, but clients running at PL1
are not expected to be supported indefinitely.)

If you're not sure, don't change the default.