Bluetooth: Controller: Refactor of ull_adv_sync_pdu_set_clear()

ull_adv_sync_pdu_set_clear does pretty much everything, causing
it to be very complex and awkward to use. In addition, it only handles
a single PDU, meaning callers have to handle the chain.
It has been replaced with simpler, more complete functions for handling
the relevant operations

Fixed issues include:

- Fragmentation of adv data over HCI is now decoupled from PDU
  fragmentation, fixing HCI/DDI/BI-13-C, LL/DDI/ADV/BV-26-C and
  LL/DDI/ADV/BV-55-C
- Adding BigInfo now preserves the PDU chain
- Enabling periodic advertising with ADI on would sometimes fail
  due to insufficient space in a single PDU to add ADI

Signed-off-by: Troels Nilsson <trnn@demant.com>