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

ST SPEAr

configname: CONFIG_PLAT_SPEAR

ARM system type
└─>ST SPEAr
In linux kernel since version 2.6.35 (release Date: 2010-08-01)  
Support for ST's SPEAr platform (SPEAr3xx, SPEAr6xx and SPEAr13xx).