Add code needed for basic suspend/resume of the XO-1 laptop. Based on

Add code needed for basic suspend/resume of the XO-1 laptop.  Based on
earlier work by Jordan Crouse, Andres Salomon, and others.

This patch incorporates all earlier feedback from Thomas Gleixner.  To
clarify a certain point (now more obvious in the code itself): On resume,
OpenFirmware returns execution to Linux in protected mode with a
kernel-compatible GDT already set up.  The changes and simplifications
suggested have all been included.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Acked-by: Andres Salomon <dilinger@queued.net>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>