dts: msm8916: import PMIC dtsi files

Import the supporting pm8916.dtsi and msm8916-pm8916.dtsi files from
upstream in preparation for switching boards over.

Taken from kernel tag v6.7

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>