bus: mhi: ep: Rename read_from_host() and write_to_host() APIs

[ Upstream commit 92710524 ]

In the preparation for adding async API support, let's rename the existing
APIs to read_sync() and write_sync() to make it explicit that these APIs
are used for synchronous read/write.

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>