Change
  dest_Loest_Prio -> IOAPIC_LOWEST_PRIORITY
  dest_Fixed -> IOAPIC_FIXED

the original names are x86 specific, while the ioapic code will be reused
for ia64.
Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>