SH5 compact register numbering in gcc -> gdb interface

[Andrew Cagney]

> sh-tdep has a lot of hardcoded 'knowledge' how simulator numbers relate
> to the layout of th register cache.  Moreover, we should loose all the
> tdep->FOO_REGNUM stuff where the value is actually a constant according
> to the simulator interface.

Just FYI, the thing that controls the internal register layout of GDB is 
[currently] the remote protocol.  If you try to wire down GDB's internal 
register numbers to match the simulator, you'll likely break GDB's 
compatibility with existing remote targets.

While this limitation is being worked on, it doesn't affect the GDB <-> 
sim maping - that can already be adjusted independant of the other 
register numbering schema.

enjoy,
Andrew