CONFIG_CPU_SUBTYPE_SH7708 is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

Support SH7708 processor

modulename: setup-sh770x.ko

configname: CONFIG_CPU_SUBTYPE_SH7708

Processor sub-type selection
└─>Support SH7708 processor
In linux kernel since version 2.6.12  
Select SH7708 if you have a 60 Mhz SH-3 HD6417708S or
if you have a 100 Mhz SH-3 HD6417708R CPU.

source code: