libxl: s/pcidev/pci and remove DEFINE_DEVICE_TYPE_STRUCT_X

libxl: s/pcidev/pci and remove DEFINE_DEVICE_TYPE_STRUCT_X

The seemingly arbitrary use of 'pci' and 'pcidev' in the code in libxl_pci.c
is confusing and also compromises use of some macros used for other device
types. Indeed it seems that DEFINE_DEVICE_TYPE_STRUCT_X exists solely because
of this duality.

This patch purges use of 'pcidev' from the libxl internal code, but
unfortunately the 'pcidevs' and 'num_pcidevs' fields in 'libxl_domain_config'
are part of the API and need to be retained to avoid breaking callers,
particularly libvirt.

DEFINE_DEVICE_TYPE_STRUCT_X is still removed to avoid the special case in
libxl_pci.c but DEFINE_DEVICE_TYPE_STRUCT is given an extra 'array' argument
which is used to identify the fields in 'libxl_domain_config' relating to
the device type.

NOTE: Some of the more gross formatting errors (such as lack of spaces after
      keywords) that came into context have been fixed in libxl_pci.c.

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