remoteproc: Add RPROC_DELETED state

Add new state RPROC_DELETED to handle synchronization
between rproc_del() and other operations on rproc. This
state represents the rproc device that has been "deleted".

CC: Loic Pallardy <loic.pallardy@st.com>
CC: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>