Documentation/cxl: Use a double line break between entries

Make it easier to read delineations between the "Description" line
break, new paragraph line breaks, and new entries.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165784324750.1758207.10379257962719807754.stgit@dwillia2-xfh.jf.intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>