tools: PCI: Add sample test script to invoke pcitest

Add a simple test script that invokes the pcitest userspace tool to perform
all the PCI endpoint tests (BAR tests, interrupt tests, read tests, write
tests and copy tests).

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>