misc: Add host side PCI driver for PCI test function device

Add PCI endpoint test driver that can verify base address register, legacy
interrupt/MSI interrupt and read/write/copy buffers between host and
device. The corresponding pci-epf-test function driver should be used on
the EP side.

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