AT91: pm: use plain cpu_do_idle() for "wait for interrupt"

For power management at91_pm_enter() routine, use the cpu_do_idle() for a
rock solid "wait for interrupt" implementation.
For AT91SAM9 ARM 926 based chips, we can exceed the cache line length as
we can access RAM even while in self-refresh mode.
We keep plain access to CP15 for at91rm9200 as this feature is not
available: instructions have to be in a single cache line.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/pm.c

@@ -258,16 +258,18 @@ static int at91_pm_enter(suspend_state_t state)
 			 * NOTE: the Wait-for-Interrupt instruction needs to be
 			 * in icache so no SDRAM accesses are needed until the
 			 * wakeup IRQ occurs and self-refresh is terminated.
+			 * For ARM 926 based chips, this requirement is weaker
+			 * as at91sam9 can access a RAM in self-refresh mode.
 			 */
 			asm("b 1f; .align 5; 1:");
 			asm("mcr p15, 0, r0, c7, c10, 4");	/* drain write buffer */
 			saved_lpr = sdram_selfrefresh_enable();
-			asm("mcr p15, 0, r0, c7, c0, 4");	/* wait for interrupt */
+			wait_for_interrupt_enable();
 			sdram_selfrefresh_disable(saved_lpr);
 			break;
 
 		case PM_SUSPEND_ON:
-			asm("mcr p15, 0, r0, c7, c0, 4");	/* wait for interrupt */
+			cpu_do_idle();
 			break;
 
 		default: