ARM: dts: msm: add CX vote for each PCIe node on MSM8996

This change adds the DT entry in each PCIe node so that
they will vote for the minimum CX power required to
maintain functionality and stability.

Change-Id: I5ace2ac61dc5b6f49cf0f948e92761aa1bcd9f5d
Signed-off-by: Tony Truong <truong@codeaurora.org>