greybus: arche-platform: Disable HUB3613 only in APB poweroff fn

HUB3613 configuration, either disable (Standby mode) or enable (HUB mode)
is related to APB. So it makes perfect sense to put both of them
together in one function.

HUB3613 enable happens only at one place, in hub_conf_delayed_work() fn,
but disable is initiated from multiple places.
Move all calls to usb3613_hub_mode_ctrl(false) to apb_poweroff().

Testing Done: Tested on DB3.5 platform.

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>