ia64/pv_ops/xen: define xen pv_init_ops for various xen initialization.

This patch implements xen version of pv_init_ops to do various
xen initialization.
This patch also includes ia64 counter part of x86 xen early printk support
patches.

Signed-off-by: Akio Takebe <takebe_akio@jp.fujitsu.com>
Signed-off-by: Alex Williamson <alex.williamson@hp.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>