arm64: dts: allwinner: h6: Pine H64: Add interrupt line for RTC

The external PCF8563 RTC chip's interrupt line is connected to the NMI
line on the SoC.

Add the interrupt line to the device tree.

Fixes: 17ebc33a

 ("arm64: allwinner: h6: add PCF8563 RTC on Pine H64 board")
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>