The ADC input pin was always configured as BDS. Modified it to configure
the correct pin.
BUG=none
TEST=On Link, "rw 0x4002451C" show 0xff instead of 0xf7.
Change-Id: I1efd5cd59ad65f55cd673529afa6153add63ecac
Refactor ADC code and move board/chip-specific part to corresponding
directories.
Implement function and console command to read Link charger current.
BUG=chrome-os-partner:7527
TEST=Read EC temperature and POT input on BDS.
Change-Id: I7fafd310ea49d9b2781f10c3453f5488da29a08a