fpga: dfl: refactor cci_enumerate_feature_devs()

fpga: dfl: refactor cci_enumerate_feature_devs()

In preparation of looking for dfls based on a vendor specific pci
capability, move the code for the default method of finding the first
dfl at offset 0 of Bar 0 to its own function.

Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Link: https://lore.kernel.org/r/20210107043714.991646-2-mdf@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>