[COMMON] watchdog: s3c2410_wdt: change clock source to rate & gate clock

[COMMON] watchdog: s3c2410_wdt: change clock source to rate & gate clock

In 4.9 kernel porting,
Conflict:
 - s3c2410wdt_set_min_max_timeout function. -> remove function
 - Clock change within probe function. -> Changed to this patch.

Clock for watchdog device is changed to open gate clock.
but there is no clockrate information in gate_watchdog clock.
so rate_watchdog clock is added to get clock rate

Change-Id: I8394ac129bd478f5de6913e8c98f12cdebf0d87e
Signed-off-by: Hyunki Koo <hyunki00.koo@samsung.com>
Signed-off-by: Changki Kim <changki.kim@samsung.com>
Signed-off-by: Kang KyungWoo <kwoo.kang@samsung.com>
Signed-off-by: Choi Jaehyoung <jkkkkk.choi@samsung.com>
Signed-off-by: Kyungwoo Kang <kwoo.kang@samsung.com>