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

Generic desktop/server/laptop

modulename: pci_dn.ko

and/or

nvram.ko

and/or

prom_init.ko

configname: CONFIG_PPC_MULTIPLATFORM

Machine type
└─>Generic desktop/server/laptop
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
Select this option if configuring for an IBM pSeries or
RS/6000 machine, an Apple machine, or a PReP, CHRP,
Maple or Cell-based machine.

source code:
arch/ppc64/kernel/