arm: imx6: cpuidle: Use raw_spinlock_t

[ Upstream commit 40d0332ec8312e9c090f0a5414d9c90e12b13611 ]

The idle call back is invoked with disabled interrupts and requires
raw_spinlock_t locks to work.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>