greybus: initialize svc connection while creating hd

Its really part of initializing the host device and is required for
every 'hd' that is created. Lets move the call to do basic
initialization of svc connection to greybus_create_hd().

Also add a comment to specify why we need to do it that early.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>