CONFIG_ARCH_OMAP15XX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

OMAP15xx Based System

modulename: gpio15xx.ko

configname: CONFIG_ARCH_OMAP15XX

Linux Kernel Configuration
└─>OMAP15xx Based System
In linux kernel since version 2.6.15 (release Date: 2006-01-02)