ARM: dts: aspeed: mowgli: Add i2c rtc device

This system uses a rx8900 compatible rtc device.

Signed-off-by: Ben Pai <Ben_Pai@wistron.com>
Link: https://lore.kernel.org/r/20210121073146.28217-1-Ben_Pai@wistron.com


Signed-off-by: Joel Stanley <joel@jms.id.au>