fpga: dfl-pci: add enumeration for feature devices

fpga: dfl-pci: add enumeration for feature devices

The Device Feature List (DFL) is implemented in MMIO and features
are linked via the DFLs. This patch enables pcie driver to prepare
enumeration information (e.g. locations of all device feature lists
in MMIO) and use common APIs provided by the Device Feature List
framework to enumerate each feature device linked.

Signed-off-by: Tim Whisonant <[email protected]>
Signed-off-by: Enno Luebbers <[email protected]>
Signed-off-by: Shiva Rao <[email protected]>
Signed-off-by: Christopher Rauer <[email protected]>
Signed-off-by: Zhang Yi <[email protected]>
Signed-off-by: Xiao Guangrong <[email protected]>
Signed-off-by: Wu Hao <[email protected]>
Acked-by: Alan Tull <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>