m68k/sun3: Convert Sun3/3x to genirq

Replace the custom irq handler that masks the irq and calls do_IRQ(), and
the unmasking in the individual handlers, by handle_level_irq().

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Sam Creasey <sammy@sammy.net>