cxl/uapi: Fix defined but not used warnings

Fix unused-const-variable warnings emitted by gcc when cxlmem.h is used
by pretty much all files except pci.c

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/163072205652.2250120.16833548560832424468.stgit@dwillia2-desk3.amr.corp.intel.com


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