soc: qcom: mem-buf: Configure the mem-buf device's DMA mask

The mem-buf device can handle memory from anywhere in the
system. This includes memory with a physical address above
32 bits, so configure the DMA mask for the mem-buf device
based on the system configuration.

Change-Id: If91bb6d8044e8e6f47994acd7e50633b46596808
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>