o Rename kernload_ap to bp_kernelload. This to introduce a common prefix

o   Rename kernload_ap to bp_kernelload. This to introduce a common prefix
    for variables that live in the boot page.
o   Add bp_trace (yes, it's in the boot page) that gets zeroed before we
    try to wake a core and to which the core being woken can write markers
    so that we know where the core was in case it doesn't wake up. The
    boot code does not yet write markers (too follow).
o   Disable the boot page translation to allow the last 4K page to be used
    for whatever we please. It would get mapped otherwise.
o   Fix kernstart in the case of SMP. The start argument is typically page
    aligned due to the alignment requirements that come with having a boot
    page. The point of using trunc_page is that we get the actual load
    address given that the entry point is immediately following the ELF
    headers. In the SMP case this ended up exactly 4K after the load
    address. Hence subtracting 1 from start.