CONFIG_ARCH_BCMBCA_BRAHMAB15 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Brahma-B15 SoCs

configname: CONFIG_ARCH_BCMBCA_BRAHMAB15

Linux Kernel Configuration
└─>Broadcom SoC Support
└─>Broadcom Broadband Carrier Access (BCA) origin SoC
└─>Brahma-B15 SoCs
In linux kernel since version 6 (release Date: 2022-10-02)  
Say Y if you intend to run the kernel on a Broadcom Broadband ARM B15
based BCA chipset.

This enables support for Broadcom BCA ARM B15 broadband chipset. Currently
only DSL chip BCM63148.