main/linux-postmarketos-qcom-msm8996: upgrade to 5.15.6
- Rebase on 5.15.6
- Fix current reading in fuel gauge, which was reading wrong values when current is negative.
- Add support for detecting charger presence and reporting battery status and health properties.
- Fix an OTG regulator bug that made its over-current protection trip when an OTG adapter is inserted into the phone first then a USB device is plugged into it.