dts: bindings: nordic-nrf-nfct-v2: Extend description

Add information about nfct node status. For cpuapp status is irrelevant
because NFCT is by default assigned to cpuapp but for cpurad node needs
to have reserved status.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>