powerpc/e500mc: Doorbells need to be taken w/exceptions disabled

We use Doorbell interrupts for IPIs and thus we need to make sure we aren't
interrupted in the process of processing the IPI.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Acked-by: NDave Liu <daveliu@freescale.com>

arch/powerpc/kernel/head_fsl_booke.S

@@ -707,7 +707,7 @@ interrupt_base:
 	EXCEPTION(0x2060, PerformanceMonitor, performance_monitor_exception, EXC_XFER_STD)
 
 #ifdef CONFIG_PPC_E500MC
-	EXCEPTION(0x2070, Doorbell, unknown_exception, EXC_XFER_EE)
+	EXCEPTION(0x2070, Doorbell, unknown_exception, EXC_XFER_STD)
 #endif
 
 	/* Debug Interrupt */