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

Mock the clear of poison by deleting the device:address entry from
the mock_poison_list[]. Behave like a real CXL device and do not fail
if the address is not in the poison list, but offer a dev_dbg()
message.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/ecf19743c6572e60971bbd078f67d520cf5bca5d.1681874357.git.alison.schofield@intel.com


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