Simplify init script by not using the device or group settings anymore,
instead always clone all repositories. This makes using the manifests
from external bsp layers easier. Internal repositories can still be
used with 'notdefault' grouping.

The --device argument is still accepted, but no longer used, to remain
backwards compatible.

Change-Id: I206d09037f40e9ce1171bddc79b7d27edfb29de4
Reviewed-by: Timo Aarnipuro <timo.aarnipuro@qt.io>