remoteproc: qcom: q6v5-mss: Add missing regulator for MSM8996

Add proxy vote for pll supply on MSM8996 SoC.

Fixes: 9f058fa2 ("remoteproc: qcom: Add support for mss remoteproc on msm8996")
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>