CONFIG_ARCH_BCM_21664 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Broadcom BCM21664 SoC family

modulename: board_bcm21664.ko

configname: CONFIG_ARCH_BCM_21664

Linux Kernel Configuration
└─>Broadcom SoC Support
└─>Broadcom Mobile SoC Selection
└─>Broadcom BCM21664 SoC family
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Enable support for the BCM21664 family, which includes
BCM21663 and BCM21664 variants.

source code:
arch/arm/mach-bcm/board_bcm21664.c