ARM: dts: msm: Add CX and MX proxy requests for holi

Add proxy-consumer properties to the VDD_CX and
VDD_MX device nodes to avoid potential issues caused by a
clock voting for a lower voltage level than what is physically
required by a clock that is initialized at a later point.

Change-Id: I3f8069ec02d03c4116159eae50b8d71f862c8f20