arm, dev: Add support for listing DMA ports in new platforms

arm, dev: Add support for listing DMA ports in new platforms

When using a Ruby memory system, the Ruby configuration scripts expect
to get a list of DMA ports to create the necessary DMA sequencers. Add
support in the utility functions that wire up devices to append DMA
ports to a list instead of connecting them to the IO bus. These
functions are currently only used by the VExpress_GEM5_V1 platform.

Change-Id: I46059e46b0f69e7be5f267e396811bd3caa3ed63
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Brad Beckmann <brad.beckmann@amd.com>