backlight: convert from legacy pm ops to dev_pm_ops

Convert drivers/video/backlight/class to use dev_pm_ops for power
management and remove Legacy PM ops hooks.

With this change, backlight 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
backlight class.

[jg1.han@samsung.com: add CONFIG_PM_SLEEP to suspend/resume functions]
Signed-off-by: Shuah Khan <shuah.kh@samsung.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Shuah Khan <shuahkhan@gmail.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Shuah Khan <shuahkhan@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>