bus: mhi: core: Add support for basic PM operations

This commit adds support for basic MHI PM operations such as
mhi_async_power_up, mhi_sync_power_up, and mhi_power_down. These
routines places the MHI bus into respective power domain states
and calls the state_transition APIs when necessary. The MHI
controller driver is expected to call these PM routines for
MHI powerup and powerdown.

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>
[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/20200220095854.4804-8-manivannan.sadhasivam@linaro.org


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