remoteproc: q6v5-mss: Vote for rpmh power domains

With rpmh ARC resources being modelled as power domains with performance
state, we need to proxy vote on these for SDM845.
Add support to vote on multiple of them, now that genpd supports
associating mutliple power domains to a device.

Tested-by: Sibi Sankar <sibis@codeaurora.org>
Reviewed-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
[bjorn: Drop device link, improve error handling, name things "proxy"]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>