CONFIG_BBC_I2C is not available for thedefaultarchitecture x86.
Result is shown for architecture sparc64
default or selected kernelversion does not have config value CONFIG_BBC_I2C.
Result is shown for kernelversion 5.4.123

UltraSPARC-III bootbus i2c controller driver

modulename: bbc.ko

configname: CONFIG_BBC_I2C

Linux/UltraSPARC Kernel Configuration
└─>General machine setup
└─>UltraSPARC-III bootbus i2c controller driver
In linux kernel since version 2.6.12  
The BBC devices on the UltraSPARC III have two I2C controllers. The
first I2C controller connects mainly to configuration PROMs (NVRAM,
CPU configuration, DIMM types, etc.). The second I2C controller
connects to environmental control devices such as fans and
temperature sensors. The second controller also connects to the
smartcard reader, if present. Say Y to enable support for these.

source code:
depends
CONFIG_PCI