CONFIG_ARCH_BCM_63XX is not available for the default architecture x86.
Result is shown for architecture arm

Broadcom BCM63xx DSL SoC

configname: CONFIG_ARCH_BCM_63XX

Linux Kernel Configuration
└─> Broadcom SoC Support
└─> Broadcom BCM63xx DSL SoC

This enables support for systems based on Broadcom DSL SoCs.
It currently supports the 'BCM63XX' ARM-based family, which includes
the BCM63138 variant.