PCI: endpoint: functions/pci-epf-test: Print throughput information

Print throughput information in KB/s after every completed transfer,
including information on whether DMA is used or not.

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>