dt-bindings: reset: syscon-reboot: Add reg property

dt-bindings: reset: syscon-reboot: Add reg property

The syscon-reboot binding used 'offset' for historical reasons. Having a
reg property is appropriate when these nodes are children of a MMIO bus.
Add a reg property and modify the constraints so that one of 'reg' or
'offset' is expected.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20241015225948.3971924-2-chris.packham@alliedtelesis.co.nz
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>