KVM: ia64: Re-organize data sturure of guests' data area

1. Increase the size of data area to 64M
2. Support more vcpus and memory, 128 vcpus and 256G memory are supported
   for guests.
3. Add the boundary check for memory and vcpu allocation.

With this patch, kvm guest's data area looks as follow:
  *
  *            +----------------------+  ------- KVM_VM_DATA_SIZE
  *            |     vcpu[n]'s data   |   |     ___________________KVM_STK_OFFSET
  *            |                      |   |    /                   |
  *            |        ..........    |   |   /vcpu's struct&stack |
  *            |        ..........    |   |  /---------------------|---- 0
  *            |     vcpu[5]'s data   |   | /       vpd            |
  *            |     vcpu[4]'s data   |   |/-----------------------|
  *            |     vcpu[3]'s data   |   /         vtlb           |
  *            |     vcpu[2]'s data   |  /|------------------------|
  *            |     vcpu[1]'s data   |/  |         vhpt           |
  *            |     vcpu[0]'s data   |____________________________|
  *            +----------------------+   |
  *            |    memory dirty log  |   |
  *            +----------------------+   |
  *            |    vm's data struct  |   |
  *            +----------------------+   |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |
  *            |   vm's p2m table  |      |
  *            |                      |   |
  *            |                      |   |
  *            |                      |   |  |
  * vm's data->|                      |   |  |
  *            +----------------------+ ------- 0
  * To support large memory, needs to increase the size of p2m.
  * To support more vcpus, needs to ensure it has enough space to
  * hold vcpus' data.
  */

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>