powerpc/irq: remove inline assembly in hard_irq_disable macro

Use WRITE_ONCE() instead of opencoding the saving of current
stack pointeur.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9f05937d8722ddd2064a7c2362d8f9000e15e1ba.1652863723.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/hw_irq.h

@@ -282,9 +282,7 @@ static inline bool pmi_irq_pending(void)
 	flags = irq_soft_mask_set_return(IRQS_ALL_DISABLED);		\
 	local_paca->irq_happened |= PACA_IRQ_HARD_DIS;			\
 	if (!arch_irqs_disabled_flags(flags)) {				\
-		asm ("stdx %%r1, 0, %1 ;"				\
-		     : "=m" (local_paca->saved_r1)			\
-		     : "b" (&local_paca->saved_r1));			\
+		WRITE_ONCE(local_paca->saved_r1, current_stack_pointer);\
 		trace_hardirqs_off();					\
 	}								\
 } while(0)