default or selected kernelversion does not have config value CONFIG_B43_DMA_MODE.
Result is shown for kernelversion 5.13-rc2

DMA (Direct Memory Access) only

configname: CONFIG_B43_DMA_MODE

Broadcom 43xx data transfer mode
└─>DMA (Direct Memory Access) only
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
Only include Direct Memory Access (DMA).
This reduces the size of the driver module, by omitting the PIO code.

selects
CONFIG_B43_DMA