libdsl: remove CONFIG_BCM_CHIP_ID
Use CONFIG_TARGET_SUBTARGET variable that already contains CHIP_ID.
This change will have no effect until following workaround is not fixed: 69f40124fa40 ("libdsl: define CONFIG_VDSL_SUPPORTED explicitly")
Use CONFIG_TARGET_SUBTARGET variable that already contains CHIP_ID.
This change will have no effect until following workaround is not fixed: 69f40124fa40 ("libdsl: define CONFIG_VDSL_SUPPORTED explicitly")