[ARM] Fix kernel/fork.c for lockdep on ARM

ARM has interrupts enabled over context switches (iow, has
__ARCH_WANT_INTERRUPTS_ON_CTXSW defined.)  The lockdep code in fork.c
 assumes that interrupts are always disabled.  Fix this wrong
assumption by making the initialisation of 'p->hardirqs_enabled'
depend on __ARCH_WANT_INTERRUPTS_ON_CTXSW.
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

kernel/fork.c

@@ -1056,7 +1056,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 #endif
 #ifdef CONFIG_TRACE_IRQFLAGS
 	p->irq_events = 0;
+#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
+	p->hardirqs_enabled = 1;
+#else
 	p->hardirqs_enabled = 0;
+#endif
 	p->hardirq_enable_ip = 0;
 	p->hardirq_enable_event = 0;
 	p->hardirq_disable_ip = _THIS_IP_;