To prepare the split of the code related to the control (ctrldev)
and the endpoint (eptdev) devices in 2 separate files:

- Rename and export the functions in rpmsg_char.h.

- Suppress the dependency with the rpmsg_ctrldev struct in the
  rpmsg_eptdev_create function.
Suggested-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: NArnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Reviewed-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220124102524.295783-2-arnaud.pouliquen@foss.st.com