CONFIG_ARCH_W90X900 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Nuvoton W90X900 CPU

configname: CONFIG_ARCH_W90X900

ARM system type
└─>Nuvoton W90X900 CPU
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Support for Nuvoton (Winbond logic dept.) ARM9 processor,
At present, the w90x900 has been renamed nuc900, regarding
the ARM series product line, you can login the following
link address to know more.