greybus: arche-apb-ctrl: Export operational fns from driver

In order to use single wake/detect line for both APB's we need to have
access to APB operational functions to parent/SVC driver.
So export coldboot, standby_boot, fw_flashing and poweroff operation
functions from the driver.

Testing Done: Tested on EVT1.2 and DB3.5 platform

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