NFC: nci: Allow to create multiple virtual nci devices

The current virtual nci driver is great for testing and fuzzing.
But it allows to create at most one "global" device which does not allow
to run parallel tests and harms fuzzing isolation and reproducibility.
Restructure the driver to allow creation of multiple independent devices.
This should be backwards compatible for existing tests.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Bongsu Jeon <bongsu.jeon@samsung.com>
Cc: Bongsu Jeon <bongsu.jeon@samsung.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20221115100017.787929-1-dvyukov@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>