Abstract IA64_FIRST_DEVICE_VECTOR/IA64_LAST_DEVICE_VECTOR since SN platforms
use a subset of the IA64 range.  Implement this by making the above macros
global variables which the platform can override in it setup code.

Also add a reserve_irq_vector() routine used by SN to mark a vector's as
in-use when that weren't allocated through assign_irq_vector().
Signed-off-by: NMark Maule <maule@sgi.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>