Bluetooth: Controller: Introduce big-endian variant for ECB

There are some use cases where all parameters are in big-endian. To
avoid excessive byte order reversals introduce a native big-endian
API.

Change-Id: I58fe9156c8819a3a43d715e70b6ba358bd2f844b
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>