cxl/memdev: Introduce cxl_class_memdev_type

cxl/memdev: Introduce cxl_class_memdev_type

In preparation for memdev's without mailbox related infrastructure,
introduce cxl_class_memdev_type as a superset of a cxl_memdev_type.
Effectively the only difference is that cxl_class_memdev_type exports
common sysfs attributes where cxl_memdev_type has none.

Related to this is all the cxl_mem_probe() paths that assume the presence
of a class device mailbox are updated to skip that requirement.

Co-developed-by: Alejandro Lucero <alucerop@amd.com>
Signed-off-by: Alejandro Lucero <alucerop@amd.com>
Signed-off-by: Dan Williams <djbw@kernel.org>
Tested-by: ALejandro Lucero <alucerop@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/20260519210158.1499795-5-djbw@kernel.org
Signed-off-by: Dave Jiang <dave.jiang@intel.com>