I also know that AMBA, with AXI and other popular bus designs from ARM are free to use without ARM CPU in the system and should be separately licensed when you use ARM ISA in your system. I can assume with high probability that most of peripherial devices like DRAM controller and others are using one of the AMBA buses.

Basically, if you use ARM CPU commercially, you are on hook to pay some not insignificant amount of money in perpetuity.

So, if Apple will continue to use ARM, they will be an ARM's customer, a significant one.