rockchip: dts: rk3399-puma: add /config/sysreset-gpio property

rockchip: dts: rk3399-puma: add /config/sysreset-gpio property

On the RK3399-Q7, we want to trigger a full platform reset (so the
various software stacks supported don't have to deal with the same
complexities over and over again) in case that anything other than a
power-on reset occurred.

To do so, this defines the /config/sysreset-gpio property and has it
point to a GPIO that will perform a power-on reset of the entire
platform.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Klaus Goger <klaus.goger@theobroma-systems.com>