of: device: Export of_device_{get_modalias, uvent_modalias} to modules

The ULPI bus can be built as a module, and it will soon be
calling these functions when it supports probing devices from DT.
Export them so they can be used by the ULPI module.

Acked-by: Rob Herring <robh@kernel.org>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>