remoteproc: Add new detach() remoteproc operation

Add an new detach() operation in order to support scenarios where
the remoteproc core is going away but the remote processor is
kept operating.  This could be the case when the system is
rebooted or when the platform driver is removed.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20210312162453.1234145-9-mathieu.poirier@linaro.org


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