interconnect: Mark all dummy functions as static inline

There are a few dummy stub functions that are not marked as static inline
yet. Currently this header file is not included in any other file outside
of drivers/interconnect/, but that might not be the case in the future.
If this file gets included and the framework is disabled, we will be see
warnings. Let's fix this in advance.

Link: https://lore.kernel.org/r/20200228145945.13579-1-georgi.djakov@linaro.org


Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>