rtc: mediatek: enhance the description for MediaTek PMIC based RTC
Give a better description for original MediaTek RTC driver as PMIC based
RTC in order to distinguish SoC based RTC. Also turning all words with
Mediatek to MediaTek here.
Cc: Eddie Huang <eddie.huang@mediatek.com> Signed-off-by: Sean Wang <sean.wang@mediatek.com> Acked-by: Eddie Huang <eddie.huang@mediatek.com> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>