CONFIG_ARCH_BCMBCA_CORTEXA9 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Cortex-A9 SoCS


Linux Kernel Configuration
└─>Broadcom SoC Support
└─>Broadcom Broadband Carrier Access (BCA) origin SoC
└─>Cortex-A9 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 A9
based BCA chipset.

This enables support for Broadcom BCA ARM A9 broadband chipset. Currently
only DSL chip BCM63138.