rtc: mt6397: Add support for the MediaTek MT6358 RTC

This add support for the MediaTek MT6358 RTC. Driver using
compatible data to store different RTC_WRTGR address offset.
This replace RTC_WRTGR to RTC_WRTGR_MT6323 in mt6323-poweroff
driver which only needed by armv7 CPU without ATF.

Signed-off-by: Ran Bi <ran.bi@mediatek.com>
Signed-off-by: Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Sebastian Reichel <sre@kernel.org>
Reviewed-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>