baylibre-acme: Add basic support for ACME revB.

Revision B of ACME hardware introduces probes with on-board at24cs02
EEPROM. Extend the ACME driver to support reading the contents of
the EEPROM via linux' sysfs interface.

Also: make the driver be able to tell the difference between revisions,
add new GPIO layout and set the shunt resistance for revB at probe
registration.

Signed-off-by: Bartosz Golaszewski <redacted>