UPSTREAM: net: qmi_wwan: rearranging to prepare for code sharing

UPSTREAM: net: qmi_wwan: rearranging to prepare for code sharing

Most of the subdriver registration code can be reused for devices
with separate control and data interfaces.  Move the code a bit
around to prepare for such reuse.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit f47cd1360f36e599815650522986673b9aa83393)

Change-Id: Ica96b7eb66a9436d11e458bff48f23835cf5d471
Signed-off-by: Ben Chan <benchan@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/35011
Reviewed-by: Olof Johansson <olofj@chromium.org>