dt-bindings: rtc: mediatek: add mt6358 and mt6366 compatible

Add mt6358 and mt6366 compatible in devicetree-binding document for
MediaTek PMIC based RTC. mt6358 and mt6366 use same compatible data
to store RTC_WRTGR address offset.

mt6358-rtc should be used as fallback for mt6366-rtc.

Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Signed-off-by: Yuchen Huang <yuchen.huang@mediatek.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220428092726.25814-2-allen-kh.cheng@mediatek.com