Bluetooth: Unify remote OOB data functions

There's no need to duplicate code for the 192 vs 192+256 variants of the
OOB data functions. This is also helpful to pave the way to support LE
SC OOB data where only 256 bit data is provided.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>