CONFIG_PM is not available for thedefaultarchitecture x86.
Result is shown for architecture m68knommu

Power Management support

modulename: pm.ko

and/or

standby.ko

and/or

main.ko

and/or

cpu.ko

and/or

suspend.ko

configname: CONFIG_PM

uClinux/68k (w/o MMU) Kernel Configuration
└─>Power management options
└─>Power Management support
In linux kernel since version 2.6.12  
Support processor power management modes