[POWERPC] spufs: provide siginfo for SPE faults

This change populates a siginfo struct for SPE application exceptions
(ie, invalid DMAs and illegal instructions).

Tested on an IBM Cell Blade.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>