driver core: Add device_is_dependent() to linux/device.h

DT implementation of fw_devlink needs this function to detect cycles. So
make it available.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>