bus: mhi: core: Add support for processing events from client device

This commit adds support for processing the MHI data and control
events from the client device. The client device can report various
events such as EE events, state change events by interrupting the
host through IRQ and adding events to the event rings allocated by
the host during initialization.

This is based on the patch submitted by Sujeev Dias:
https://lkml.org/lkml/2018/7/9/988

Signed-off-by: Sujeev Dias <sdias@codeaurora.org>
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>
[mani: splitted the data transfer 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/20200220095854.4804-11-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>