arm64: dts: ls1028a: fix reboot node

The reboot register isn't located inside the DCFG controller, but in its
own RST controller. Fix it.

Fixes: 8897f325 ("arm64: dts: Add support for NXP LS1028A SoC")
Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>