MIPS: jz4740: DTS: Probe the jz4740-rtc driver from devicetree

Now that the jz4740-rtc driver supports devicetree, we can add a
devicetree node for it.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>