ARM11: partial support for standard ARM register interfaces.

ARM11: partial support for standard ARM register interfaces.

This provides "standard" ARM register support -- with twenty or
more shadow registers on top of what this code now handles, but
properly associated with the various core modes -- parallel to
the current register code.  That is, the current code is stilil
managing the "current" registers; the new code shadows them.

You can see all the registers with "arm reg", modify the shadows
like "r8_fiq" or "sp_abt" with "reg", and see them get properly
written back when you step.  (Just don't do that with any of the
registers managed by the "old" code ...)

It also switches to using more standard code, relying on those
standard registers, in two places:  (a) the poll status display,
which now shows core state (ARM/Thumb/...) and mode (Supervisor,
IRQ, etc); and (b) GDB register access.

So it's not a full migration, there are warts -- every place that
touches the old register cache is a potential bug -- but it's a
small more-or-less-comprehensible step that's even somewhat useful.
Later patches complete the migration.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>