remoteproc: sysmon: Wait for SSCTL service to come up

The SSCTL service comes up after a finite time when the remote Q6 comes
out of reset. Any graceful shutdowns requested during this period will
be a NOP and abrupt tearing down of the glink channel might lead to pending
transactions on the remote Q6 side and will ultimately lead to a fatal
error. Fix this by waiting for the SSCTL service when a graceful shutdown
is requested.

Fixes: 1fb82ee8 ("remoteproc: qcom: Introduce sysmon")
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1657022900-2049-7-git-send-email-quic_sibis@quicinc.com