libxl/xl: Use libxl_vcpuinfo_destroy

libxl/xl: Use libxl_vcpuinfo_destroy

Replaces libxl_free_vcpu_list.

The ->cpumap field is now always a unique allocation rather than each
being an offset into the cpumap allocated in the first
libxl_device_pci in the list.

Refactor vcpulist so that the two cases can share more code.

[PATCH 15 of 16 of
 libxl: autogenerate type definitions and destructor functions]

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>