bus: mhi: ep: Introduce async read/write callbacks

[ Upstream commit 8b786ed8 ]

These callbacks can be implemented by the controller drivers to perform
async read/write operation that increases the throughput.

For aiding the async operation, a completion callback is also introduced.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Stable-dep-of: c7d0b2db ("bus: mhi: ep: Do not allocate memory for MHI objects from DMA zone")
Signed-off-by: Sasha Levin <sashal@kernel.org>