This ensures a ".dtb" PE section makes it into the UKI so systemd-stub
can install the correct devicetree for use by the Linux kernel. This is
often needed on systems that boot with u-boot since the devicetree used
by u-boot is often a paired down version of what the Linux kernel needs.
On those kinds of boards, the lack of this PE section means that u-boot
will end up installing its internal devicetree into the UEFI
configuration table, which is what the Linux kernel ends up using.
Previously any user-provided config for boot.uki.settings would need to
either specify a full set of config for ukify or a combination of
mkOptionDefault to merge the "settings" attribute set with the module's
defaults and then mkOverride or mkForce to override a contained
attribute.
Now it is possible to trivially override parts of the module's default
config, such as the initrd or kernel command line, but overriding the
full set of settings now requires mkOverride / mkForce.
