This is mostly a preparatory commit to later be able to read the
deviceinfo from multiple places. It has a bit better encapsulation,
and makes the functions methods, so that they can update deviceinfo
file in-place.
This greatly reduces the chance accidentally adding dependencies to the
other (currently unused) variables later on. Getting away from depending
on deviceinfo has a lot of benefits, but mainly it helps offload
device-specific boot configuration to boot-deploy. Handling those
complexities in a shell script is often nicer.
Also, reducing the need to handle variables that contain lists means
that this app doesn't have to worry about how to merge/handle multiple
versions of those. That might be useful later if mkinitfs has to read
deviceinfo config from multiple deviceinfo files.
For example, trying to figure out how to merge these two things is...
ehhh...
a_modules_initfs="abc bar banana bazz"
b_modules_initfs="foo bar bazz bar2 guava"
An earlier revision of this patch had test for invalid lines, but I
decided to remove it because deviceinfo is sourced by so many things in
pmOS that it should be /very/ obvious that there are invalid lines or
other garbage in the file.
I also tried to make the parser fairly forgiving if it does encounter
things that don't meet the deviceinfo "spec", so that mkinitfs will try
as hard as it can to make an initfs.
