PCI: epf-test: Simplify DMA support checks

PCI: epf-test: Simplify DMA support checks

There is no need to have each read, write and copy test functions check
for the FLAG_USE_DMA flag against the DMA support status indicated by
epf_test->dma_supported. Move this test to the command handler function
pci_epf_test_cmd_handler() to check once for all cases.

Link: https://lore.kernel.org/r/20230415023542.77601-13-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>