[IA64] Implement guest_os_type for ia64

[IA64] Implement guest_os_type for ia64

This makes use of the domain config option guest_os_type for
ia64 and removes the backing for the previous ACPI based
mechanism used previously.  A user wanting optimal performance
for a specific type of OS guest running in an HVM domain should
make use of this new option.  See updated xmexmaple.vti for
available options.  All supported OSes should always work using
the default option or leaving the option unspecified.  Originally
based on patch from Zhang Xin.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>