leds: Convert led class driver from legacy pm ops to dev_pm_ops

Convert drivers/leds/led-class to use dev_pm_ops for power management and
remove Legacy PM ops hooks. With this change, led class registers
suspend/resume callbacks via class->pm (dev_pm_ops) instead of Legacy
class->suspend/resume. When __device_suspend() runs call-backs, it will
find class->pm ops for the led class.

Signed-off-by: Shuah Khan <shuah.kh@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>