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

Broadcom SoC

modulename: board_bcm281xx.ko

and/or

bcm_kona_timer.ko

configname: CONFIG_ARCH_BCM

Linux Kernel Configuration
└─>Broadcom SoC
In linux kernel since version 3.1 (release Date: 2011-10-24)  
This enables support for system based on Broadcom SoCs.
It currently supports the 'BCM281XX' family, which includes
BCM11130, BCM11140, BCM11351, BCM28145 and
BCM28155 variants.

source code:
selects
CONFIG_ARCH_REQUIRE_GPIOLIB
CONFIG_ARM_ERRATA_754322
CONFIG_ARM_ERRATA_764369
CONFIG_ARM_GIC
CONFIG_CPU_V7
CONFIG_CLKSRC_OF
CONFIG_GENERIC_CLOCKEVENTS
CONFIG_GENERIC_TIME
CONFIG_GPIO_BCM
CONFIG_SPARSE_IRQ
CONFIG_TICK_ONESHOT
CONFIG_CACHE_L2X0


is selected by
CONFIG_ARCH_BCM2835