RFA: Add xscale machine to config.sub

[Ben Elliston]

Hi Nick,

     I would like to apply the following patch to allow the targets
     'xscale-elf' and 'xscale-coff' to be configured.  The patch also
     tidies up the lines in config.sub a little bit, so that all of the
     different ARM ports are together on one line instead of being mixed
     up.

Sure.  I'll apply this patch to the official versions of these files, also.
As an aside, I'm hoping to clean up much of config.sub in the near future,
so thanks for getting things rolling.

Ben