Bluetooth: controller: Adding user ext. anchor point move to ctrl/CPR

Adding support for allowing user extension code to support deferring
anchor point moves. Refactored LLCP only.
Note: This is NOT supported by LEGACY LLCP impl.
KConfig'd by BT_CTLR_USER_CPR_ANCHOR_POINT_MOVE
Modified ll_conn_update API, to accommodate passing offsets
Modified CPR/CU context data structure
Modified CPR/CU procedure to handle anchor point move wait state
Fixed up unit tests, adding anchor point move cases to CPR/CU test

Signed-off-by: Erik Brockhoff <erbr@oticon.com>