gdb: clean up some things in features/Makefile

gdb: clean up some things in features/Makefile

Clean up some things I noticed:

 - we generate a regformats/microblaze-with-stack-protect.dat file.  I
   don't think this is used.  It could be used by a GDBserver built for
   Microblaze, but GDBserver isn't ported to Microblaze.  So I don't
   think that's used at all.  Remove the entry in features/Makefile and
   the file itself.

 - There are a bunch of *-expedite values in features/Makefile for
   architectures for which we don't generate dat files.  AFAIK, these
   *-expedite values are only used when generating dat files.  Remove
   those that are not necessary.

 - 32bit-segments.xml is not listed in the Makfile, but it's used.  This
   means that it wouldn't get re-generated if we were to change how C
   files are generated from the XML.  It looks like it was simply
   forgotten, add it.

Change-Id: I112d00db317102270e1df924473c37122ccb6c3a