smb138x-charger: use SW based comparison for connector health

The hardware based threshold comparison requires thermal regulation to
be active. This is a problem for layouts which connect USBIN rather than
MID to the SMB138X since the thermal regulation will throttle the ICL in
the USBIN case.

Read the connector temperature ADC and compare against the thresholds
in software instead of enabling thermal regulation.

Change-Id: I9ecda675947fc6c82a8c8b67d0c9d930365ad02e
Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>