greybus: arche-platform: Enter ACTIVE state only from OFF state

Make sure that, transition to active state happens only from OFF state.
Instead of imposing the restriction to user-space, driver internally
switches to OFF state and then to ACTIVE state.

Testing Done: Tested on EVT1.5 platform.

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