greybus: arche-platform: Add state variable to driver data

This is preparation for operational state support.
So in order to provide operational state transitions, driver needs to
maintain state. So add 'enum arche_platform_state' variable to
'struct arche_platform_drvdata'

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>