Add support for kexec-hardboot

"Allows hard booting (i.e., with a full hardware reboot) to a kernel
previously loaded in memory by kexec.  This works around the problem of
soft-booted kernel hangs due to improper device shutdown and/or
reinitialization."
More info in /arch/arm/Kconfig.

Original author: Mike Kasick <mike@kasick.org>
These patches are ported from Asus TF201, to which it
was ported by Jens Andersen <jens.andersen@gmail.com>.

Change-Id: Ibee734f61ffa97577bfbcdd9a8cd567bd2d89f32