Revert patches that break libxl API

Revert patches that break libxl API

This patch reverts eight patches from staging.

The offending patch is the one that introduced libxl_pci_bdf (last one
in the list). The rest depend on that patch so they are also reverted.

8bf0fab14256 "libxl / libxlu: support 'xl pci-attach/detach' by name"
e1141654c374 "docs/man: modify xl-pci-configuration(5) to add 'name' field to PCI_SPEC_STRING"
93c16ae47baf "xl: support naming of assignable devices"
5ab684cb3e4d "libxl: introduce libxl_pci_bdf_assignable_add/remove/list/list_free(), ..."
66c2fbc6e82b "libxl: convert internal functions in libxl_pci.c..."
f73c5dd56d78 "docs/man: modify xl(1) in preparation for naming of assignable devices"
96ed6ff29741 "libxlu: introduce xlu_pci_parse_spec_string()"
929f23114061 "libxl: introduce 'libxl_pci_bdf' in the idl..."

Signed-off-by: Wei Liu <wl@xen.org>