CONFIG_ARCH_BCM4908 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm64
default or selected kernelversion does not have config value CONFIG_ARCH_BCM4908.
Result is shown for kernelversion 6.9.2

Broadcom BCM4908 family

configname: CONFIG_ARCH_BCM4908

Linux Kernel Configuration
└─>Platform selection
└─>Broadcom BCM4908 family
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
This enables support for the Broadcom BCM4906, BCM4908 and
BCM49408 SoCs. These SoCs use Brahma-B53 cores and can be
found in home routers.

selects
CONFIG_GPIOLIB

is selected by
CONFIG_PHY_BRCM_USB