tools/testing/cxl: Mock the Inject Poison mailbox command

Mock the injection of poison by storing the device:address entries in
mock_poison_list[]. Enforce a limit of 8 poison injections per memdev
device and 128 total entries for the cxl_test mock driver.

Introducing the mock_poison[] list here, makes it available for use in
the mock of Clear Poison, and the mock of Get Poison List.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/f6b7f03541eaa8c2260d3eafadd04afe3f0d7962.1681874357.git.alison.schofield@intel.com


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