It's easier to extend and it centralises the config parsing. In other
places we will no longer need to use `g_str_equal` to match these values,
a `switch` statement will be sufficient.
We use a similar trick to having a `sysroot -> .` symlink on the real root
here to support both /boot on root as well as on a separate filesystem. No
matter how it's mounted `/boot/xyz` will always refer to the file you'd
expect.
This is nicer than my previous attempts at this because there's no
configuration nor auto-detection required.
William Manley