gn: make device/battery build on embedded linux
gn: make device/battery build on embedded linux

The logic for when to include the linux dbus implementation
falls into three cases: chromeos, non-chromeos linux with
dbus, and non-chromeos linux without dbus.

By using just the is_chromeos, is_linux and use_dbus
variables, this code will also build successfully on
embedded linux targets.

Review URL: https://codereview.chromium.org/1674233002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#374654}

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