powerpc/32: Enter exceptions with MSR_EE unset

All exceptions handlers know when to reenable interrupts, so
it is safer to enter all of them with MSR_EE unset, except
for syscalls.

Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[splited out from benh RFC patch]

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/head_44x.S

@@ -281,7 +281,7 @@ interrupt_base:
 	FP_UNAVAILABLE_EXCEPTION
 #else
 	EXCEPTION(0x2010, BOOKE_INTERRUPT_FP_UNAVAIL, \
-		  FloatingPointUnavailable, unknown_exception, EXC_XFER_EE)
+		  FloatingPointUnavailable, unknown_exception, EXC_XFER_STD)
 #endif
 	/* System Call Interrupt */
 	START_EXCEPTION(SystemCall)
@@ -290,7 +290,7 @@ interrupt_base:
 
 	/* Auxiliary Processor Unavailable Interrupt */
 	EXCEPTION(0x2020, BOOKE_INTERRUPT_AP_UNAVAIL, \
-		  AuxillaryProcessorUnavailable, unknown_exception, EXC_XFER_EE)
+		  AuxillaryProcessorUnavailable, unknown_exception, EXC_XFER_STD)
 
 	/* Decrementer Interrupt */
 	DECREMENTER_EXCEPTION
@@ -298,7 +298,7 @@ interrupt_base:
 	/* Fixed Internal Timer Interrupt */
 	/* TODO: Add FIT support */
 	EXCEPTION(0x1010, BOOKE_INTERRUPT_FIT, FixedIntervalTimer, \
-		  unknown_exception, EXC_XFER_EE)
+		  unknown_exception, EXC_XFER_STD)
 
 	/* Watchdog Timer Interrupt */
 	/* TODO: Add watchdog support */