Cosmetic rearrangement of boot2 addresses.
Rework of BERI boot2 to allow it to relocate itself from wherever it starts
executing to a low-memory address (above exception vectors and below spin
tables).  The previous version required that boot2 be found at specific
address -- which was fine if we just expect boot2 to be found in flash at a
predefined address, but is less useful if we want to load it via JTAG.