sparc32, sun4m: bugfix in SMP IPI traphandler

Three new IPIs were introduced by commit
ecbc42b7 ("sparc32, sun4m:
Implemented SMP IPIs support for SUN4M machines"), the
old handler was already prepared for IPIs but handled only
IRQ14 and IRQ13, this patch adds support for the new IPI at
IRQ12.

The IPI trap handler looks at the mask rather than the
pending IRQ/IPI, this bug may have masked the problem
above, introduced by the same commit.

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>