rpmsg: Move RPMSG_ADDR_ANY in user API

As the RPMSG_ADDR_ANY is a valid src or dst address that can be set by
user applications, migrate its definition in user API.

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20210311140413.31725-3-arnaud.pouliquen@foss.st.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>