arm64: dts: qcom: sdm845-oneplus-*: add fuel gauge

The OnePlus 6 and 6T feature a BQ27411 fuel gauge for reading the
battery stats. Enable it and add a simple battery to document the
battery specs of each device.

Signed-off-by: Caleb Connolly <caleb@connolly.tech>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220120184546.499030-1-caleb@connolly.tech