arm64: fix access to preempt_count from assembly code

preempt_count is defined as an int. Oddly enough, we access it
as a 64bit value. Things become interesting when running a BE
kernel, and looking at the current CPU number, which is stored
as an int next to preempt_count. Like in a per-cpu interrupt
handler, for example...

Using a 32bit access fixes the issue for good.

Cc: Matthew Leach <matthew.leach@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/entry.S

@@ -311,14 +311,14 @@ el1_irq:
 #endif
 #ifdef CONFIG_PREEMPT
 	get_thread_info tsk
-	ldr	x24, [tsk, #TI_PREEMPT]		// get preempt count
-	add	x0, x24, #1			// increment it
-	str	x0, [tsk, #TI_PREEMPT]
+	ldr	w24, [tsk, #TI_PREEMPT]		// get preempt count
+	add	w0, w24, #1			// increment it
+	str	w0, [tsk, #TI_PREEMPT]
 #endif
 	irq_handler
 #ifdef CONFIG_PREEMPT
-	str	x24, [tsk, #TI_PREEMPT]		// restore preempt count
-	cbnz	x24, 1f				// preempt count != 0
+	str	w24, [tsk, #TI_PREEMPT]		// restore preempt count
+	cbnz	w24, 1f				// preempt count != 0
 	ldr	x0, [tsk, #TI_FLAGS]		// get flags
 	tbz	x0, #TIF_NEED_RESCHED, 1f	// needs rescheduling?
 	bl	el1_preempt
@@ -509,15 +509,15 @@ el0_irq_naked:
 #endif
 	get_thread_info tsk
 #ifdef CONFIG_PREEMPT
-	ldr	x24, [tsk, #TI_PREEMPT]		// get preempt count
-	add	x23, x24, #1			// increment it
-	str	x23, [tsk, #TI_PREEMPT]
+	ldr	w24, [tsk, #TI_PREEMPT]		// get preempt count
+	add	w23, w24, #1			// increment it
+	str	w23, [tsk, #TI_PREEMPT]
 #endif
 	irq_handler
 #ifdef CONFIG_PREEMPT
-	ldr	x0, [tsk, #TI_PREEMPT]
-	str	x24, [tsk, #TI_PREEMPT]
-	cmp	x0, x23
+	ldr	w0, [tsk, #TI_PREEMPT]
+	str	w24, [tsk, #TI_PREEMPT]
+	cmp	w0, w23
 	b.eq	1f
 	mov	x1, #0
 	str	x1, [x1]			// BUG