remoteproc: qcom: Add shutdown-ack irq

Add shutdown-ack irq handling required for sysmon shutdown for
Q6V5 MSS on SDM845/MSM8996 and for WCSS Q6V5 on QCS404 SoC.

Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
[bjorn: Revert back to qcom_add_sysmon_subdev returning a sysmon object]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>