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

IBM Legacy iSeries

modulename: e2a.ko

configname: CONFIG_PPC_ISERIES

Machine type
└─>IBM Legacy iSeries
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
source code:
arch/powerpc/lib/e2a.c

depends
CONFIG_PPC64 |
| CONFIG_PPC_MULTIPLATFORM or CONFIG_CLASSIC32 or CONFIG_PPC64