rom_set_rom_callback() function

Set ROM callback function The only currently supported callback_number is 0 which sets the callback used for the secure_call API. A callback pointer of 0 deletes the callback function, a positive callback pointer (all valid function pointers are on RP2350) sets the callback function, but a negative callback pointer can be passed to get the old value without setting a new value. If successful, returns >=0 (the existing value of the function pointer on entry to the function).