CONFIG_MACH_SPEAR300 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
SPEAr300 Machine support with Device Tree
modulename: spear300.ko
configname: CONFIG_MACH_SPEAR300
Linux Kernel Configuration
└─>SPEAr3xx Implementations
└─>SPEAr300 Machine support with Device Tree
In linux kernel since version 2.6.35 (release Date: 2010-08-01)
Supports ST SPEAr300 machine configured via the device-tree