power: qpnp-fg-gen4: Add support to configure battery thermistor interval

Add a DT property "qcom,fg-batt-therm-freq" to configure the
battery thermistor measurement sampling interval. This is to help
with battery temperature measurement based on the needs.

Change-Id: I7acfdac201bcedcd3425b39d825267d6ae83932d
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>