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

Renesas ARM SoCs (non-multiplatform)

configname: CONFIG_ARCH_SHMOBILE_LEGACY

ARM system type
└─>Renesas ARM SoCs (non-multiplatform)
In linux kernel since version 3.14 (release Date: 2014-03-30)  
Support for Renesas ARM SoC platforms using a non-multiplatform
kernel. This includes the SH-Mobile, R-Mobile, EMMA-Mobile, R-Car
and RZ families.