powerpc: Enforce a non-spe kernel build even on broken compilers

Those two are required on my fresh gcc 4.3.1.

Signed-off-by: Thiemo Seufer <ths@linutronix.de>
Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>