bus: mhi: core: Add support for MHI suspend and resume

Add support for MHI suspend and resume states. While at it, the
mhi_notify() function needs to be exported as well.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20200427075829.9304-2-manivannan.sadhasivam@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>