power: supply: bq256xx: Apply TS_IGNORE from devicetree

TS_IGNORE is default off in bq256xx chip. For some HW which doesn't have
the NTC, we need to set TS_IGNORE to 1 to make the charge work. The new
"ti,no-thermistor" is introduced to toggle it.

Signed-off-by: Hermes Zhang <chenhuiz@axis.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>