paravirtualize ivt.S which implements fault handler in hand written
assembly code.
They includes sensitive or performance critical privileged instructions.
So they need paravirtualization.

Cc: Keith Owens <kaos@ocs.com.au>
Cc: tgingold@free.fr
Cc: Akio Takebe <takebe_akio@jp.fujitsu.com>
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>