libxl: add 'name' field to 'libxl_device_pci' in the IDL...

libxl: add 'name' field to 'libxl_device_pci' in the IDL...

... and modify libxl_pci_bdf_assignable_add/remove/list() to make use of it.

libxl_pci_bdf_assignable_add() will store the name of the device in xenstore
if the field is specified (i.e. non-NULL) and libxl_pci_bdf_assignable_remove()
will remove devices specified only by name, looking up the BDF as necessary.

libxl_pci_bdf_assignable_list() will also populate the 'name' field if a name
was stored by libxl_pci_bdf_assignable_add().

NOTE: This patch also fixes whitespace in the declaration of 'libxl_device_pci'
      in the IDL.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Acked-by: Wei Liu <wl@xen.org>