Bluetooth: CSIP: Update documentation for CSIP crypto functions

The encryption functions should document the expect byte order of
inputs and the byte order of the outputs.

The sef and sdf functions were also using an older, and incorrect,
description of the input, as it only takes the LTK as per CSIP 1.0.0

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>