misc: pci_endpoint_test: Use streaming DMA APIs for buffer allocation

Use streaming DMA APIs (dma_map_single/dma_unmap_single) for buffers
transmitted/received by the endpoint device instead of allocating
a coherent memory. Also add default_data to set the alignment to
4KB since dma_map_single might not return a 4KB aligned address.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>