leds: leds-asic3: switch to using SIMPLE_DEV_PM_OPS

Switch to using SIMPLE_DEV_PM_OPS  macro to declare the driver's
pm_ops. It reduces code size. Also, CONFIG_PM_SLEEP is added to
suspend/ resume functions to prevent build warnings when
CONFIG_PM_SLEEP is not selected.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>