CONFIG: remove #ifdef __ia64__ from the x86 arch tree

CONFIG: remove #ifdef __ia64__ from the x86 arch tree

__ia64__ really really should not be defined in the x86 arch subtree,
so remove it from xen/include/public/arch-x86/hvm/save.h

This in turn allows the removal of VIOAPIC_IS_IOSAPIC, as x86 does not
use streamlined {IO,L}APICs, allowing for the removal of more code
from the x86 tree.

Changes since v2:
 *  Leave the EOI register write protected by VIOAPIC_VERSION_ID >=
    0x20.  Currently, only version 0x11 is emulated, but leave this
    correct code in place in case a decision is make to emulate the
    newer version.

Changes since v1:
 *  Refresh patch following the decision not to try emulating a
    version 0x20 IOAPIC

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>