ARM: dts: msm: Mark the mem-buf device on the trusted VM as a consumer

The mem-buf driver on the trusted VM is meant to be used as
a channel for requesting memory from another VM, and should
not be used for allocating memory for other VMs, so mark the
mem-buf device as a consumer.

Change-Id: I92a035106620e2c913006dfb7a15007ba563288e