dt-bindings: qpnp-fg-gen4: Support configuring 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: I370cb1507291869d66fe111f2acf02150f008482
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>