power: qpnp-fg: add dt prop for therm delay

qcom,fg-therm-delay controls the time to delay before biasing the
battery thermistor.

Add this device tree property to expose this setting.

CRs-Fixed: 920744
Change-Id: I44d6210d7d53a5948b88da5a164ef8f9cef428d6
Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>