CONFIG_CPU_SUBTYPE_SH7751 is not available for the selected architecture x86.
Result is shown for architecture sh

Support SH7751 processor

modulename: setup-sh7750.ko

and/or

pci-sh7751.ko

configname: CONFIG_CPU_SUBTYPE_SH7751

Linux Kernel Configuration
└─>Processor selection
└─>Support SH7751 processor
In linux kernel since version 2.6.12 )
Select SH7751 if you have a 166 Mhz SH-4 HD6417751 CPU,
or if you have a HD6417751R CPU.
source code:
/arch/sh/drivers/pci/