ARM: dts: msm: add MX entries for PCIe on sdxlemur

To properly support PCIe Gen4 on sdxlemur, PCIe needs to vote
and scale MX rails accordingly. Add the required MX entries to
enable PCIe bus driver to do so for sdxlemur.

Change-Id: Ia56142013d07c9a811f5357e8ce29fdb3c76dd39