OPAL runs in big endian, so we need to rfid into it to switch endian
atomically when branching to it, and we need to do the
RETURN_TO_NATIVE_ENDIAN dance when it returns to us.
Sponsored by: Tag1 Consulting, Inc.
OPAL is a dedicated firmware acting as a hypervisor.
Add generic functions to provide all access.
Created by: Nathan Whitehorn <nw@freebsd.org>
Submitted by: Wojciech Macek <wma@freebsd.org>