Bluetooth: controller: Add window widening for CIS/CIG

Program CIG ticker with window widening drift. Introduce vendor specific
conversion macros allowing sub-microsecond resolution in the
accumulation of window widening drift per interval.

Calculation of window_widening_max_us is done for NSE<3, and must be
adjusted in the LLL before use, if the first CIS in the CIG has a
NSE>=3. In that case window_widening_max_us shall be limited to one sub
interval.

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