PCI: endpoint: functions/pci-epf-test: Add DMA support to transfer data

Use dmaengine API and add support for transferring data using DMA.

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>