CONFIG_BOARD_BCM963XX is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Generic Broadcom 963xx boards

modulename: board_bcm963xx.ko

configname: CONFIG_BOARD_BCM963XX

Board support
└─>Generic Broadcom 963xx boards
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
source code:
arch/mips/bcm63xx/boards/board_bcm963xx.c
selects
CONFIG_SSB