tools/testing/cxl: Move cxl_test resources to the top of memory

A recent QEMU upgrade resulted in collisions between QEMU's chosen
location for PCI MMIO and cxl_test's fake address location for emulated
CXL purposes. This was great for testing resource collisions, but not so
great for continuing to test the nominal cases. Move cxl_test to the
top-of-memory where it is less likely to collide with other resources.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165603886021.551046.12395967874222763381.stgit@dwillia2-xfh
Signed-off-by: Dan Williams <dan.j.williams@intel.com>