CONFIG_MACH_U300_SPIDUMMY is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

SSP/SPI dummy chip

modulename: dummyspichip.ko

configname: CONFIG_MACH_U300_SPIDUMMY

Linux Kernel Configuration
└─>ST-Ericsson AB U300/U330/U335/U365 Platform
└─>SSP/SPI dummy chip
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
This creates a small kernel module that creates a dummy
SPI device to be used for loopback tests. Regularly used
to test reference designs. If you're not testing SPI,
you don't need it. Selecting this will activate the
SPI framework and ARM PL022 support.

source code: