greybus: arche-apb-ctrl: Do not export any gpios

With addition of operational state in driver, user/developer
can switch to FW flashing state through sysfs. So no need to
export any gpios to userspace now.

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>