Building with the attached random configuration file,
sound/built-in.o: In function `rt5645_i2c_probe':
rt5645.c:(.text+0x8f63f): undefined reference to `devm_regmap_init_i2c'
sound/built-in.o: In function `rt5645_i2c_driver_exit':
rt5645.c:(.exit.text+0x327): undefined reference to `i2c_del_driver'
sound/built-in.o: In function `rt5645_i2c_driver_init':
rt5645.c:(.init.text+0x78f): undefined reference to `i2c_register_driver'