Bluetooth: Controller: Fix ISO Sync Receiver time reservation calc

Fix missing ISO Synchronized Receiver radio event time
reservation that did not calculate for all the subevents.

Introduce BT_CTLR_SYNC_ISO_RESERVE_MAX Kconfig option to
allow using a minimal time reservation if needed to allow
other role to pre-empt ISO Synchronized Receiver in
pre-transmission and control subevents.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>