platform/surface: aggregator: Move subsystem hub drivers to their own module

platform/surface: aggregator: Move subsystem hub drivers to their own module

Split out subsystem device hub drivers into their own module. This
allows us to load the hub drivers separately from the registry, which
will help future DT/OF support.

While doing so, also remove a small bit of code duplication.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20220624205800.1355621-3-luzmaximilian@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>