power: smb135x-charger: Add a DT node to disable BMD algorithm

BMD (battery missing detection) can use either the THERM pin or
a specific BMD algorithm. Add a node to select either of them.

SMB135x drops the SYS_OK when battery is missing and APSD is
incomplete.

In the THERM pin configuration, when there is no battery connected
and there is a valid VBATT (externally regulated) the SYS_OK goes low
when an input is inserted. This is because as soon the input is
inserted SMB detects a missing battery even before APSD is complete and
drops SYS_OK. To avoid this use the BMD algorithm which relies on VBATT
instead of THERM for missing battery detection. As VBATT is good, SMB
detects a valid battery and SYS_OK is not dropped.

Note that the VBATT based BMD or THERM algorithm runs only when charging
begins.

Change-Id: I35357e454599a70789da1d810f0c2b0fcae18e59
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>