[IA64] Clean up VTi memory initialization logic

[IA64] Clean up VTi memory initialization logic

This patch makes the logic in setup_guest() more clear.
domain_translate_gpfn_list() is now gone, so we can make
memory initializtion code simple.
Xend passes memory size which is a sum of normal memory
size and GFW memory to QEMU and Libxc. This patch fixes
this issue.

Signed-off-by: Zhang Xin <xing.z.zhang@intel.com>