PM / devfreq: exynos4: Use devm_devfreq_* function using device resource management

This patch uses devm_devfreq_add_device()/devm_devfreq_register_opp_notifier()
to control automatically the resource of devfreq.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>