cxl: Refactor user ioctl command path from mds to mailbox

cxl: Refactor user ioctl command path from mds to mailbox

With 'struct cxl_mailbox' context introduced, the helper functions
cxl_query_cmd() and cxl_send_cmd() can take a cxl_mailbox directly
rather than a cxl_memdev parameter. Refactor to use cxl_mailbox
directly.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20250204220430.4146187-2-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>