target/ppc: 405: Debug exception cleanup

target/ppc: 405: Debug exception cleanup

The current Debug exception dispatch is the BookE one, so it is
different from the 405. We effectively don't support the 405 Debug
exception.

This patch removes the BookE code and moves the DEBUG into the "not
implemented" block.

Note that there is in theory a functional change here since we now
abort when a Debug exception happens. However, given how it was never
implemented, I don't believe this to have ever been dispatched for the
405.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20220118184448.852996-11-farosas@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>