Bluetooth: Introduce public big-endian AES API

There may be use cases where input and output is in big-endian rather
than little-endian. Introduce a native big-endian API to avoid
excessive byte order reversals in these cases.

Change-Id: Ia7b3e01bb0a07c4560b23f60c2f615ec614eb431
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>