qpnp-fg-gen3: add support for configuring slope limit coefficients

Slope limit coefficient is used to define the maximum change in
battery SOC. There is a requirement to configure slope limit
coefficient based on charging status and battery temperature
threshold. Add support for it through the following properties.

- qcom,slope-limit-temp-threshold
- qcom,slope-limit-coeffs

Possibe values allowed for slope limit coefficient is 0 to 31.

Change-Id: I41eacb13734f1692a16c1b011c58a488e46515ec
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>