soc: qcom: mem-buf: Add support for restricting memory transfers

The mem-buf driver follows a supplier and consumer model
to enforce what the instance of the driver on a particular
Virtual Machine (VM) can and cannot do. These roles are
conveyed through the qcom,mem-buf-capabilities property.

A driver on a VM that has the supplier capability is able
to lend and share memory to other VMs, but cannot request
memory from another VM.

In the other direction, a VM with consumer capability is
only capable of requesting memory from other VMs, but cannot
satisfy memory requests from other VMs.

Change-Id: I1d258bdaafbbdb020831afc85c47f44a5ec93940
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>