Bluetooth: controller: Introduce config for avoiding SDU fragmentation

The CIS Central uses the algorithm described in BT Core 5.4 Vol 6,
Part G, Section 2.2 to calculate the Max_PDU value for framed mode.

However, HAP needs the Max_PDU to be calculated according to "Core
enhancement for ISOAL CR" coming with the "Atlanta" update. With this
update, the fragmentation is controlled via a parameter at CIG creation.

Enabling CONFIG_BT_CTLR_CONN_ISO_AVOID_SEGMENTATION will set the
ISO_Interval to 7.5 ms for a 10 ms framed CIG, and calculate Max_PDU to
45/65 for 16/24 kHz.

Signed-off-by: Morten Priess <mtpr@oticon.com>