fwctl/cxl: Fix uuid_t usage in uapi

The uuid_t type is kernel internal, and Paul reports the following build
error when it is used in a uapi header:

    usr/include/cxl/features.h:59:9: error: unknown type name ‘uuid_t’

Create a uuid type (__uapi_uuid_t) compatible with the longstanding
definition uuid/uuid.h for userspace builds, and use uuid_t directly for
kernel builds.

Fixes: 9b8e73cd ("cxl: Move cxl feature command structs to user header")
Link: https://patch.msgid.link/r/174430961702.617339.13963021112051029933.stgit@dwillia2-xfh.jf.intel.com


Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Closes: http://lore.kernel.org/f6489337-67c7-48c8-b48a-58603ec15328@paulmck-laptop


Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504050434.Eb4vugh5-lkp@intel.com/


Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>