* Add ability to fetch and report peripheral battery levels
on split centrals.
* Add additional support for adding a new Battery Level
service to split centrals that exposes fetched peripheral
battery levels to connected hosts.
Co-authored-by: Peter Johanson <peter@peterjohanson.com>
* Previous version of multiple overrides of the default value of ZMK_USB
were problematic. Move to using board _defconfig files for the
defaults for those, along with proper `depends on` for ZMK_USB that
accounts for split and split roles.
* Split centrals to scan with their identity so they receive direct
advertising packets.
* Split peripherals to use direct advertising if they have an existing
bond to a split central.
