CONFIG_MACH_U300_SPIDUMMY is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_U300_SPIDUMMY.
Result is shown for kernelversion 6.8.2

SSP/SPI dummy chip

modulename: dummyspichip.ko

configname: CONFIG_MACH_U300_SPIDUMMY

Linux Kernel Configuration
└─>ST-Ericsson U300 Series
└─>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: