bus: mhi: core: Add device hardware reset support

The MHI specification allows to perform a hard reset of the device
when writing to the SOC_RESET register. It can be used to completely
restart the device (e.g. in case of unrecoverable MHI error).

This is up to the MHI controller driver to determine when this hard
reset should be used, and in case of MHI errors, should be used as
a reset of last resort (after standard MHI stack reset).

This function is a stateless function, the MHI layer do nothing except
triggering the reset by writing into the right register(s), this is up
to the caller to ensure right mhi_controller state (e.g. unregister the
controller if necessary).

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>