mfd: mt6397: Implement wake handler and suspend/resume to handle wake up event

Implement .irq_set_wake() to get who is wakeup source and setup on suspend/reumse. Enable
mt6393_irq as wake up source properly to pinctrl by enable_irq_wake()/enable_irq_wake().

Signed-off-by: Henry Chen <henryc.chen@mediatek.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>