mfd: sec: Cleanup unused RTC fields: ono, WTSR and SMPL

The WTSR (Watchdog Timer Software Reset) and SMPL (Sudden Momentary
Power Loss) were removed from rtc-s5m driver because they were not used.
Remove them (and on/off interrupt) from main MFD driver and header.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>