Adding MHL api's for device discovery and registering callback mechanism.USB driver use these API's for synchronization with MHL driver. Change-Id: I0846951302e3b5f5d20d566c92c2f224528ca455 Signed-off-by: Manoj Rao <manojraj@codeaurora.org> Signed-off-by: Abhishek Kharbanda <akharban@codeaurora.org>