fpga: dfl-pci: rectify ReST formatting

fpga: dfl-pci: rectify ReST formatting

Commit fa41d10589be ("fpga: dfl-pci: locate DFLs by PCIe vendor specific
capability") provides documentation to the FPGA Device Feature List (DFL)
Framework Overview, but introduced new documentation warnings:

  ./Documentation/fpga/dfl.rst:
    505: WARNING: Title underline too short.
    523: WARNING: Unexpected indentation.
    523: WARNING: Blank line required after table.
    524: WARNING: Block quote ends without a blank line; unexpected unindent.

Rectify ReST formatting in ./Documentation/fpga/dfl.rst.

Tested-by: Tom Rix <trix@redhat.com>
Acked-by: Moritz Fischer <mdf@kernel.org>
Acked-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20210111112113.27242-1-lukas.bulwahn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>