arm64: dts: Added syscon-reboot node for FSL's LS2080A SoC

Added sys-reboot node to the FSL's LS2080A SoC DT to leverage
the ARM-generic reboot mechanism for this SoC. This mechanism
is enabled through CONFIG_POWER_RESET_SYSCON.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Olof Johansson <olof@lixom.net>