soc: qcom: rpmhpd: Mark mx as a parent for cx

Specify the active + sleep and active-only MX power domains as
the parents of the corresponding CX power domains. This will ensure that
performance state requests on CX automatically generate equivalent requests
on MX power domains.

This is used to enforce a requirement that exists for various
hardware blocks on SDM845 that MX performance state >= CX performance
state for a given operating frequency.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>