dt-bindings: nfc: nxp,nci: document NXP PN547 binding

NXP PN547 NFC controller seems to be compatible with the NXP NCI and
there already DTS files using two compatibles.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211011073934.34340-3-krzysztof.kozlowski@canonical.com


Signed-off-by: Rob Herring <robh@kernel.org>