Bluetooth: Refactor UUID-16 list generation into its own function

We will need to create three separate UUID lists in the EIR data (for
16, 32 and 128 bit UUIDs) so the code is easier to follow if each list
is generated in their own function.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>