tools: PCI: Add 'd' command line option to support DMA

Add a new command line option 'd' to use DMA for data transfers.
It should be used with read, write or copy commands.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Alan Mikhak <alan.mikhak@sifive.com>