nios2: Use preempt_schedule_irq

Follow aa0d5326 ("ia64: Use preempt_schedule_irq") and use
preempt_schedule_irq instead of enabling/disabling interrupts and
messing around with PREEMPT_ACTIVE in the nios2 low-level preemption
code ourselves. Also get rid of the now needless re-check for
TIF_NEED_RESCHED, preempt_schedule_irq will already take care of
rescheduling.

This also fixes the following build error when building with
CONFIG_PREEMPT:

arch/nios2/kernel/built-in.o: In function `need_resched':
arch/nios2/kernel/entry.S:374: undefined reference to `PREEMPT_ACTIVE'

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/kernel/entry.S

@@ -365,30 +365,14 @@ ENTRY(ret_from_interrupt)
 	GET_THREAD_INFO	r1
 	ldw	r4, TI_PREEMPT_COUNT(r1)
 	bne	r4, r0, restore_all
-
-need_resched:
 	ldw	r4, TI_FLAGS(r1)		/* ? Need resched set */
 	BTBZ	r10, r4, TIF_NEED_RESCHED, restore_all
 	ldw	r4, PT_ESTATUS(sp)	/* ? Interrupts off */
 	andi	r10, r4, ESTATUS_EPIE
 	beq	r10, r0, restore_all
-	movia	r4, PREEMPT_ACTIVE
-	stw	r4, TI_PREEMPT_COUNT(r1)
-	rdctl	r10, status		/* enable intrs again */
-	ori	r10, r10 ,STATUS_PIE
-	wrctl	status, r10
-	PUSH	r1
-	call	schedule
-	POP	r1
-	mov	r4, r0
-	stw	r4, TI_PREEMPT_COUNT(r1)
-	rdctl	r10, status		/* disable intrs */
-	andi	r10, r10, %lo(~STATUS_PIE)
-	wrctl	status, r10
-	br	need_resched
-#else
-	br	restore_all
+	call	preempt_schedule_irq
 #endif
+	br	restore_all
 
 /***********************************************************************
  * A few syscall wrappers