Spinning the disks down across a 'halt' on Alpha is even
worse than doing that on reboot on i386 (assuming the
boot device is IDE disk).
Typically, the sequence to boot another kernel is:
# halt
kernel shuts down, firmware re-initializes,
then on firmware prompt we type something like
boot -file new_kernel_image.gz
Unfortunately, the firmware does not expect the IDE drive
to be in standby mode and reports 'bootstrap failure' on
the first and all subsequent boot attempts until the
drive spins up, which is extremely annoying and
confuses users a lot.
This patch allows architectures override the default
behavior (don't spin the disks down on reboot only)
in asm/ide.h.