remoteproc: qcom: q6v5-mss: add powerdomains to MSM8996 config

MSM8996 follows the rest of MSS devices and requires a vote on MX and CX
power domains. Add corresponding entry to the device data.

Fixes: 4760a896 ("remoteproc: q6v5-mss: Vote for rpmh power domains")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>