Add width and endianness attributes to data areas in software lists (nw)
Update neogeo.xml to take advantage of them.

For regular rom loading we try to autodetect the appropriate endianness and
width by matching the region tag to a device with a device_memory_interface;
this is generally not doable for software lists because the regions are
children of some slot device and thus not siblings of the devices in the root
driver (i.e. "cartslot1:maincpu" rather than "maincpu") So you have to
specify the width and endianness manually for now.

Anyone who has spare time, feel welcome to byteswap every single entry
in megadriv.xml and update them to use this :-)