dt-bindings: iio: add support for calibrated bat_therm channel

Add support for calibrated bat_therm channel on charger PMICs
PM8350B and PM7325B, which has more accuracy than default bat_therm
channel.

Change-Id: Id24e187c5a83519f9913457e871429bf729d9213
Signed-off-by: Jishnu Prakash <quic_jprakash@quicinc.com>