All of these stubs at the end pop the stack and tell the LOAPIC
that we are at EOI. Put this in common code which falls through to
_IntExit(). Saves 8 bytes per static IRQ stub. There is also small
constant savings in the common code for dynamic IRQs.
Change-Id: If17e9f105928a4251a2cb3fc0d192649c1c4d84b
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>