feat(plat/mediatek/mt8186): add RTC drivers

Add RTC drivers for EOSC calibration.

TEST=build pass
BUG=b:202871018

Signed-off-by: Yuchen Huang <yuchen.huang@mediatek.corp-partner.google.com>
Change-Id: Ib48c07204c4a614072ba710c042794b59e8a902a
3 files changed