Flush and invalidate data caches

Implement a weak linked function to handle the data cache.
If the specific device is implementing a data cache the function should
be overriden with device specific implementation of the flush/invalidate
functions to make sure that the cache is properly maintained with
regards to the NPU DMA transaction.

Change-Id: I175644ef37bee62cc77d789d2b7bc3073e72ea5a