target-cris: Override do_interrupt for pre-v32 CPU cores

Instead of forwarding from cris_cpu_do_interrupt() to do_interruptv10(),
override CPUClass::do_interrupt with crisv10_cpu_do_interrupt() in the
newly introduced class_init functions.

Acked-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>