PCI: endpoint: pci-epf-test: Advertise dynamic inbound mapping support

PCI: endpoint: pci-epf-test: Advertise dynamic inbound mapping support

The doorbell test requires the EPC driver to support dynamic inbound
mapping so the host can map the doorbell target address into a BAR
aperture.

Expose epc_features->dynamic_inbound_mapping via a new
CAP_DYNAMIC_INBOUND_MAPPING bit in the pci-epf-test capability register,
so the host-side pci_endpoint_test driver can detect missing support and
return -EOPNOTSUPP instead of running the test fruitlessly.

Suggested-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20260215150334.3391943-2-den@valinux.co.jp