rtc: fsl-ftm-alarm: fix freeze(s2idle) failed to wake

Use dev_pm_set_wake_irq() instead of flag IRQF_NO_SUSPEND to enable
wakeup system feature for both freeze(s2idle) and mem(deep).

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200601071914.36444-1-ran.wang_1@nxp.com