CONFIG_ARCH_BCM4908 is not available for the default architecture x86.
Result is shown for architecture arm64
default or selected kernelversion does not have config value CONFIG_ARCH_BCM4908.
Result is shown for kernelversion 6.0-rc7

Broadcom BCM4908 family

configname: CONFIG_ARCH_BCM4908

Linux Kernel Configuration
└─> Platform selection
└─> Broadcom BCM4908 family

This enables support for the Broadcom BCM4906, BCM4908 and
BCM49408 SoCs. These SoCs use Brahma-B53 cores and can be
found in home routers.