ARM: imx: Add comments to tzic_enable_waker()

Add additional comments to the tzic_enable_wake() funciton to
clarify its intended usage.
Signed-off-by: NRobert Lee <rob.lee@linaro.org>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>

arch/arm/plat-mxc/tzic.c

@@ -190,6 +190,10 @@ void __init tzic_init_irq(void __iomem *irqbase)
  * tzic_enable_wake() - enable wakeup interrupt
  *
  * @return			0 if successful; non-zero otherwise
+ *
+ * This function provides an interrupt synchronization point that is required
+ * by tzic enabled platforms before entering imx specific low power modes (ie,
+ * those low power modes beyond the WAIT_CLOCKED basic ARM WFI only mode).
  */
 int tzic_enable_wake(void)
 {