main/postmarketos-mkinitfs: Make USB configfs attrs customizable
Some devices' downstream kernels may have different RNDIS/functionfs drivers (e.g. QCRNDIS) that require different values for some configfs gadget attributes. Make it possible to customize with deviceinfo file from device- package.
The idea is that each device package may optionally specify a bunch of new
deviceinfo_usb_* variables in its
deviceinfo file to customize the way it is visible on USB bus.
The ability to change RNDIS function name (
deviceinfo_usb_rndis_function) is essential to make downstream sdm660 based device to appear on USB bus.
While at it, make
serialnumber customizable too, so that it will be possible for example to make PineTab appear as PineTab on USB bus, not as
Google Inc. Nexus 4 (fastboot) (see USB ID database).