CHROMIUM: Input: atmel_mxt_ts - split hw_version from fw_version sysfs attribute

CHROMIUM: Input: atmel_mxt_ts - split hw_version from fw_version sysfs attribute

This driver's sysfs attribute is pretty dubious, however, for the fw & hw
version let's follow the 'one ASCII value per attribute' guidelines:
(For sysfs style, see Documentation/filesystems/sysfs.txt).

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chrome-os-partner:8474
TEST=cat /sys/bus/i2c/drivers/atmel_mxt_ts/<bus>/hw_version
  # Confirm same as "Family ID: %d Variant ID: %d" in /var/log/messages
TEST=cat /sys/bus/i2c/drivers/atmel_mxt_ts/<bus>/fw_version
  # Compare same as "Major.Minor.Build: %d.%d.%d" in /var/log/messages

Change-Id: Ib751d0d15c9fa6a59cad2ce3b09564b4ebf216a7
Reviewed-on: https://gerrit.chromium.org/gerrit/20906
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>