cxl/Documentation: Update references to attributes added in v6.0

Prior to Linus deciding that the kernel that following v5.19 would be
v6.0, the CXL ABI documentation already referenced v5.20. In preparation
for updating these entries update the kernel version to v6.0.

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Gregory Price <gregory.price@memverge.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Fan Ni <fan.ni@samsung.com>
Link: https://lore.kernel.org/r/167601993360.1924368.14122892663883462813.stgit@dwillia2-xfh.jf.intel.com


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