Draft: soc-qcom-sdm845: prepare modem on boot

Upcoming Modem Manager releases will enable support for the Modems found in SDM845 devices, however some early initialisation needs to happen before Modem Manager starts to configure the data port and select a SIM.

Right now this script will always activate the first available SIM card and configure the endpoints for mobile data.

This script is not intended to be a permanent solution, as Modem Manager should be able to handle this setup itself (e.g. through gnome settings UI).

Don't merge this until after MM and libqmi gets updated.

Cc: @sdm845-mainline