CONFIG_CPU_SUBTYPE_SH7751R is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

Support SH7751R processor

modulename: pci-sh7751.ko

and/or

setup-sh7750.ko

configname: CONFIG_CPU_SUBTYPE_SH7751R

Processor sub-type selection
└─>Support SH7751R processor
In linux kernel since version 2.6.16 (release Date: 2006-03-19)  
source code:
/arch/sh/drivers/pci/
selects
CONFIG_CPU_SH4