bus: mhi: core: Add support for PM state transitions

This commit adds support for transitioning the MHI states as a
part of the power management operations. Helpers functions are
provided for the state transitions, which will be consumed by the
actual power management routines.

This is based on the patch submitted by Sujeev Dias:
https://lkml.org/lkml/2018/7/9/989



Signed-off-by: Sujeev Dias <sdias@codeaurora.org>
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>
[jhugo: removed dma_zalloc_coherent() and fixed several bugs]
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
[mani: splitted the pm patch and cleaned up for upstream]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
Link: https://lore.kernel.org/r/20200220095854.4804-7-manivannan.sadhasivam@linaro.org


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