This finishes the basic switchover to the new register code,
for everything except the debug registers.  (And maybe we
shouldn't have a cache for *those* which works this way...)

The context save/restore code now uses the new code, but
it's in a slightly different sequence.  That should be fine
since the R0/PC/CPSR stuff is all that really matters (and
if we can update those, we can update the rest).

Now there's no longer a way any code can be confused about
which copy of "r1" (etc) to use.

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