tools/testing/cxl: Add partition support

In support of testing DPA allocation mechanisms in the CXL core, the
cxl_test environment needs to support establishing and retrieving the
'pmem partition boundary.

Replace the platform_device_add_resources() method for delineating DPA
within an endpoint with an emulated DEV_SIZE amount of partitionable
capacity. Set DEV_SIZE such that an endpoint has enough capacity to
simultaneously participate in 8 distinct regions.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165603887411.551046.13234212587991192347.stgit@dwillia2-xfh


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