remoteproc: qcom: q6v5-pil: Explicitly get mss_restart line

Explicitly get mss_restart to facilitate adding PDC reset line
for modem on SDM845 SoCs

Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>