[PATCH 0 of 6] Add support for a VM generation ID virtual device (v2)

[Paul Durrant <paul.durrant@citrix.com>]

The following is a revised patch series to add support for a
VM generation ID virtual device for HVM guests.
The basic requirements of this device are as follows:

- It must be exposed somewhere in ACPI namespace with a _CID of
  "VM_Gen_Counter".
- It must also include a _DDN of "VM_Gen_Counter".
- It must contain a _HID object but no particular value is
  required.
- It must expose a package called ADDR which evaluates to two
  integers; the first being the low order 32-bits of a guest
  physical address (GPA), the second by the high order 32-bits of
  the GPA. This GPA is the address of an 8-byte aligned 8-byte
  buffer containing the VM generation ID.
  This buffer must not be in ranges supported as AddressRangeMemory
  or AddressRangeACPI and must not be mapped by any PTE with caching
  disabled.

The semantics of the VM generation ID itself are left up to the tools
but it must be possible to change it each time the VM is booted,
migrated, or restored from a saved image.

Patch 1 adds the device and an acpi_info field to allow population
of the ADDR package.
Patch 2 adds ctype infrastructure to hvloader in preparation for...
Patch 3 adds all the code to plumb the value of a new 'generation_id'
parameter in the VM config through to the VM generation id buffer at
VM boot time.
Patch 4 adds an implementation of sprintf() to hvmloader.
Patch 5 adds an implementation of xenstore-write to hvmloader.
Patch 6 adds support for tracking the address of the VM generation id
buffer (via xenstore) across save/restore or migrate and updating the
value of the buffer with the value from the VM config file.